17 Education & Technology (YQ) 20-F9 Apr 212020 FY Annual report (foreign)Financial data

Company Profile

Document and Entity Information

Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2020shares
Document Information [Line Items]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Registrant Name	17 EDUCATION & TECHNOLOGY GROUP INC.
Entity Central Index Key	0001821468
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-39742
Entity Incorporation, State or Country Code	E9
Entity Address, Address Line One	16/F, Block B, Wangjing Greenland Center
Entity Address, City or Town	Chaoyang District, Beijing
Entity Address, Country	CN
Document Annual Report	true
Document Transition Report	false
Document Shell Company Report	false
Document Registration Statement	false
Document Accounting Standard	U.S. GAAP
Entity Common Stock Shares Outstanding	480,183,070
Business Contact
Document Information [Line Items]
Entity Address, Address Line One	16/F, Block B
Entity Address, City or Town	Chaoyang District, Beijing
Entity Address, Country	CN
Contact Personnel Name	Michael Chao Du
Entity Address, Address Line Two	Wangjing Greenland Center
City Area Code	+86
Local Phone Number	10 5945 1082
Contact Personnel Email Address	michael.du@17zuoye.com
American Depositary Shares
Document Information [Line Items]
Security Exchange Name	NASDAQ
Trading Symbol	YQ
Title of 12(b) Security	American Depositary Shares, two representing five Class A ordinary shares, par value US$0.0001 per share
Class A Ordinary Shares
Document Information [Line Items]
Security Exchange Name	NASDAQ
Title of 12(b) Security	Class A ordinary shares, par value US$0.0001 per share
No Trading Symbol Flag	true
Entity Common Stock Shares Outstanding	421,729,902
Class B Ordinary Shares
Document Information [Line Items]
Entity Common Stock Shares Outstanding	58,453,168

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)
Current assets
Cash and cash equivalents	¥ 2,834,962	$ 434,477	¥ 653,859
Restricted cash	170	26	34,843
Prepaid expenses and other current assets	211,448	32,406	66,311
Amounts due from a related party			2,611
Total current assets	3,046,580	466,909	757,624
Non-current assets
Property and equipment, net	105,223	16,126	65,169
Right-of-use assets	200,157	30,675	78,637
Other non-current assets	37,782	5,790	16,859
TOTAL ASSETS	3,389,742	519,500	918,289
Current liabilities
Short-term borrowings (including short-term borrowings of the consolidated VIEs without recourse to the Group of RMB9,000 and nil as of December 31, 2019 and 2020, respectively)			85,000
Accrued expenses and other current liabilities (including accrued expenses and other current liabilities of the consolidated VIEs without recourse to the Group of RMB151,413 and RMB213,481 as of December 31, 2019 and 2020, respectively)	539,787	82,725	309,031
Deferred revenue, current (including deferred revenue, current of the consolidated VIEs without recourse to the Group of RMB224,092 and RMB571,827 as of December 31, 2019 and 2020, respectively)	596,307	91,388	243,521
Operating lease liabilities, current (including operating lease liabilities, current of the consolidated VIEs without recourse to the Group of RMB28,179 and RMB46,835 as of December 31, 2019 and 2020, respectively)	69,409	10,637	43,152
Total current liabilities	1,205,503	184,750	680,704
Non-current liabilities
Deferred revenue, non-current (including deferred revenue, non- current of the consolidated VIEs without recourse to the Group of RMB652 and RMB1,982 as of December 31, 2019 and 2020, respectively)	1,982	304	652
Operating lease liabilities, non-current (including operating lease liabilities, non-current of the consolidated VIEs without recourse to the Group of RMB18,325 and RMB56,427 as of December 31, 2019 and 2020, respectively)	118,107	18,101	21,282
TOTAL LIABILITIES	1,325,592	203,155	702,638
Commitments and Contingencies (Note 17)
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			4,675,579
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares			37
Additional paid-in capital	10,653,403	1,632,705
Accumulated other comprehensive income	49,614	7,604	88,216
Accumulated deficit	(8,639,180)	(1,324,012)	(4,602,437)
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	2,064,150	316,345	(4,459,928)
TOTAL LIABILITIES, MEZZANINE EQUITY AND SHAREHOLDERS' (DEFICIT) EQUITY	3,389,742	519,500	918,289
Series B Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			330,817
Series B+ Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			516,469
Series C Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			504,721
Series D Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			1,227,905
Series E Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			2,095,667
Class A Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	275	42
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	275	42
Class B Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	38	6
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	¥ 38	$ 6
Series A Convertible Preferred Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Series A convertible preferred shares (US$0.0001 par value; 22,257,215 and nil shares authorized as of December 31, 2019 and 2020, respectively, 17,085,275 and nil issued and outstanding as of December 31, 2019 and 2020, respectively)			¥ 54,256

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)shares	Dec. 31, 2020USD ($)$ / sharesshares	Jan. 01, 2020CNY (¥)	Dec. 31, 2019CNY (¥)shares	Dec. 31, 2019$ / shares	Jan. 01, 2019CNY (¥)	Jan. 31, 2018shares
Short-term borrowings \| ¥				¥ 85,000
Accrued expenses and other current liabilities	¥ 539,787	$ 82,725		309,031
Deferred revenue, current	596,307	91,388	¥ 243,521	243,521		¥ 75,737
Operating lease liabilities, current	69,409	10,637		43,152
Deferred revenue, non-current	1,982	304		652
Operating lease liabilities, non-current	¥ 118,107	$ 18,101		¥ 21,282
Convertible redeemable preferred shares, shares issued	301,298,172	301,298,172
Convertible redeemable preferred shares, shares outstanding				267,841,063
Common stock, par value \| $ / shares		$ 0.0001			$ 0.0001
Common stock, shares authorized				509,631,372
Common stock, shares issued				57,864,058
Common stock, shares outstanding				57,864,058
Series B Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value \| $ / shares		$ 0.0001			0.0001
Convertible redeemable preferred shares, shares authorized				34,815,112
Convertible redeemable preferred shares, shares issued	34,815,112	34,815,112		34,544,762
Convertible redeemable preferred shares, shares outstanding				34,544,762
Series B+ Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value \| $ / shares		$ 0.0001			0.0001
Convertible redeemable preferred shares, shares authorized				54,083,288
Convertible redeemable preferred shares, shares issued				54,083,288
Convertible redeemable preferred shares, shares outstanding				54,083,288
Series C Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value \| $ / shares		$ 0.0001			0.0001
Convertible redeemable preferred shares, shares authorized				50,195,203
Convertible redeemable preferred shares, shares issued	50,195,203	50,195,203		50,195,203
Convertible redeemable preferred shares, shares outstanding				50,195,203
Series D Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value \| $ / shares		$ 0.0001			0.0001
Convertible redeemable preferred shares, shares authorized				50,193,243
Convertible redeemable preferred shares, shares issued	50,193,243	50,193,243		50,193,243
Convertible redeemable preferred shares, shares outstanding				50,193,243
Series E Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value \| $ / shares		$ 0.0001			0.0001
Convertible redeemable preferred shares, shares authorized				78,824,567
Convertible redeemable preferred shares, shares issued	78,824,567	78,824,567		78,824,567			78,824,567
Convertible redeemable preferred shares, shares outstanding				78,824,567
Class A Ordinary Shares
Common stock, par value \| $ / shares		$ 0.0001			0.0001
Common stock, shares authorized	1,300,000,000	1,300,000,000
Common stock, shares issued	421,729,902	421,729,902
Common stock, shares outstanding	421,729,902	421,729,902
Class B Ordinary Shares
Common stock, par value \| $ / shares		$ 0.0001			0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	58,453,168	58,453,168
Common stock, shares outstanding	58,453,168	58,453,168
Series A Convertible Preferred Shares
Preferred stock, par value \| $ / shares		$ 0.0001			$ 0.0001
Preferred stock, shares authorized				22,257,215
Preferred stock, shares issued				17,085,275
Preferred stock, shares outstanding				17,085,275
VIEs
Short-term borrowings \| ¥				¥ 9,000
Accrued expenses and other current liabilities \| ¥	¥ 213,481			151,413
Deferred revenue, current \| ¥	571,827			224,092
Operating lease liabilities, current \| ¥	46,835			28,179
Deferred revenue, non-current \| ¥	1,982			652
Operating lease liabilities, non-current \| ¥	¥ 56,427			¥ 18,325

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)¥ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019CNY (¥)¥ / sharesshares	Dec. 31, 2018CNY (¥)¥ / sharesshares
Income Statement [Abstract]
Net revenues	¥ 1,294,371	$ 198,371	¥ 406,245	¥ 310,706
Cost of revenues	(495,671)	(75,965)	(173,476)	(104,967)
Gross profit	798,700	122,406	232,769	205,739
Operating expenses:
Sales and marketing expenses	(1,097,932)	(168,265)	(583,818)	(303,492)
Research and development expenses	(614,770)	(94,218)	(491,266)	(398,627)
General and administrative expenses	(420,114)	(64,385)	(157,793)	(203,129)
Total operating expenses	(2,132,816)	(326,868)	(1,232,877)	(905,248)
Loss from operations	(1,334,116)	(204,462)	(1,000,108)	(699,509)
Interest income	8,422	1,291	23,834	33,980
Interest expense	(2,925)	(448)	(485)
Foreign currency exchange gain (loss)	(15,557)	(2,384)	12,907	8,576
Other income, net	4,268	654	102	882
Loss before provision for income tax	(1,339,908)	(205,349)	(963,750)	(656,071)
Income tax expenses \| ¥
Net loss	(1,339,908)	(205,349)	(963,750)	(656,071)
Accretion of convertible redeemable preferred shares	(2,837,991)	(434,941)	(600,535)	(244,371)
Net loss available to ordinary shareholders of 17 Education & Technology Group Inc.	¥ (4,177,899)	$ (640,290)	¥ (1,564,285)	¥ (900,442)
Net loss per ordinary share
Basic and diluted \| (per share)	¥ (44.68)	$ (6.85)	¥ (27.25)	¥ (18.50)
Weighted average shares used in calculating net loss per ordinary share
Basic and diluted \| shares	93,503,437	93,503,437	57,410,827	48,676,298

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Statement Of Income And Comprehensive Income [Abstract]
Net loss	¥ (1,339,908)	$ (205,349)	¥ (963,750)	¥ (656,071)
Other comprehensive income (loss), net of tax of nil:
Change in cumulative foreign currency translation adjustments	(38,602)	(5,916)	(11,972)	69,566
Total comprehensive loss attributable to 17 Education & Technology Group Inc.	¥ (1,378,510)	$ (211,265)	¥ (975,722)	¥ (586,505)

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) EQUITY ¥ in Thousands, $ in Thousands	CNY (¥)shares	USD ($)shares	Ordinary SharesCNY (¥)shares	Additional Paid-in CapitalCNY (¥)	Additional Paid-in CapitalUSD ($)	Accumulated Other Comprehensive Income (Loss)CNY (¥)	Accumulated Other Comprehensive Income (Loss)USD ($)	Accumulated DeficitCNY (¥)	Accumulated DeficitUSD ($)	Class A Ordinary SharesCNY (¥)shares	Class A Ordinary SharesUSD ($)shares	Class B Ordinary SharesCNY (¥)shares	Class B Ordinary SharesUSD ($)shares	Series A Convertible Preferred Sharesshares
Beginning Balance at Dec. 31, 2017	¥ (2,256,992)		¥ 26			¥ 30,622		¥ (2,341,896)
Beginning Balance, Shares at Dec. 31, 2017 \| shares			41,343,304											54,256
Net loss	(656,071)							(656,071)
Share-based compensation	123,530			¥ 123,530
Shares issuance in relation to share-based compensation	7		¥ 7
Shares issuance in relation to share based compensation, Shares \| shares			10,646,244
Repurchase and cancellation of vested options	(11,883)			(11,883)
Accretion of convertible redeemable preferred shares	(244,371)			(111,647)				(132,724)
Foreign currency translation adjustments	69,566					69,566
Ending Balance at Dec. 31, 2018	(2,976,214)		¥ 33			100,188		(3,130,691)
Ending Balance, Shares at Dec. 31, 2018 \| shares			51,989,548											54,256
Net loss	(963,750)							(963,750)
Share-based compensation	93,090			93,090
Shares issuance in relation to share-based compensation	4		¥ 4
Shares issuance in relation to share based compensation, Shares \| shares			5,874,510
Repurchase and cancellation of vested options	(551)			(551)
Accretion of convertible redeemable preferred shares	(600,535)			(92,539)				(507,996)
Foreign currency translation adjustments	(11,972)					(11,972)
Ending Balance at Dec. 31, 2019	(4,459,928)		¥ 37			88,216		(4,602,437)
Ending Balance, Shares at Dec. 31, 2019 \| shares			57,864,058											54,256
Net loss	(1,339,908)	$ (205,349)						(1,339,908)
Share-based compensation	356,038			356,038
Repurchase and cancellation of ordinary share for settlement of amount due from a related party and others	(2,831)			(2,831)
Repurchase and cancellation of ordinary share for settlement of amount due from a related party and others, Shares \| shares			(115,324)
Repurchase and cancellation of vested options	(528)			(528)
Accretion of convertible redeemable preferred shares	(2,837,991)			(141,156)				(2,696,835)
Exercise of stock options	¥ 195		¥ 14	181
Exercise of stock options, Shares \| shares	6,052,167	6,052,167	20,135,999							242,999	242,999
Issuance of ordinary shares upon the initial public offering ("IPO") and exercising the over-allotment option by the underwriters	¥ 2,023,593			2,023,542						¥ 51
Issuance of ordinary shares upon initial public offering and exercising the over-allotment option by the underwriters, Shares \| shares										78,775,000	78,775,000
Conversion of convertible preferred shares upon the IPO	8,363,098			8,417,146						¥ 206		¥ 2
Conversion of ordinary share, Series A Convertible preferred shares and convertible redeemable preferred shares upon initial public offering, Shares \| shares										314,807,446	314,807,446	3,305,651	3,305,651	(54,256)
Re-designation of ordinary shares into Class A and Class B ordinary shares upon the IPO			¥ (51)							¥ 18		¥ 33
Re-designation of ordinary shares into Class A and Class B ordinary shares upon the IPO, Shares \| shares			(77,884,733)							27,867,521	27,867,521	50,017,212	50,017,212
Shares issuance in relation to warrant exercised	1,014			1,014
Shares issuance in relation to warrant exercised, Shares \| shares										36,936	36,936
Shares issuance in connection with vesting of restricted share units (Note 10)				(3)								¥ 3
Shares issuance in connection with vesting of restricted share units (Note 10), Shares \| shares												5,130,305	5,130,305
Foreign currency translation adjustments	(38,602)					(38,602)
Ending Balance at Dec. 31, 2020	¥ 2,064,150	$ 316,345		¥ 10,653,403	$ 1,632,705	¥ 49,614	$ 7,604	¥ (8,639,180)	$ (1,324,012)	¥ 275	$ 42	¥ 38	$ 6
Ending Balance, Shares at Dec. 31, 2020 \| shares										421,729,902	421,729,902	58,453,168	58,453,168

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) EQUITY (Parenthetical) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)
Statement Of Stockholders Equity [Abstract]
Issuance cost	¥ 28,153

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	¥ (1,339,908)	$ (205,349)	¥ (963,750)	¥ (656,071)
Adjustments to reconcile net loss to net cash generated from operating activities
Depreciation of property and equipment	39,700	6,084	22,675	15,760
Share-based compensation	356,038	54,565	93,090	123,530
Foreign currency remeasurement gain	(38)	(6)	(291)	(3,902)
Noncash lease expenses	62,997	9,655	41,814	21,248
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(145,137)	(22,243)	(28,176)	(24,736)
Operating lease right-of-use assets	(184,517)	(28,278)	(63,829)	(35,777)
Other non-current assets	(2,760)	(423)	(4,164)	(3,486)
Accrued expenses and other current liabilities	213,439	32,711	82,691	112,704
Deferred revenue	354,116	54,271	168,288	23,974
Operating lease liabilities	123,082	18,863	20,364	7,891
Net cash used in operating activities	(522,988)	(80,150)	(631,288)	(418,865)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of short-term investments				(20,000)
Proceeds from maturity of short-term investments			20,000	5,000
Purchase of property and equipment	(89,504)	(13,717)	(48,594)	(33,947)
Net cash used in investing activities	(89,504)	(13,717)	(28,594)	(48,947)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the IPO and from exercising the over-allotment option by the underwriters	2,051,695	314,436
Payment of the IPO issuance cost	(18,469)	(2,830)
Payment to repurchase of ordinary shares				(21,082)
Payment to repurchase of the Series A convertible preferred shares				(4,730)
Repurchase and cancellation of vested options	(528)	(81)	(551)	(11,883)
Proceeds from exercise of share options	195	30
Net proceeds from the issuance of convertible redeemable preferred shares	3,274,069			1,588,067
Proceeds from short-term borrowings			85,000
Repayment of short-term borrowings	(85,000)	(13,027)
Net cash generated from financing activities	2,797,421	428,724	84,449	1,550,372
Effect of exchange rate changes	(38,499)	(5,902)	(11,709)	72,803
Net increase (decrease) in cash and cash equivalents and restricted cash	2,146,430	328,955	(587,142)	1,155,363
Cash, cash equivalents and restricted cash at beginning of the year	688,702	105,548	1,275,844	120,481
Cash, cash equivalents and restricted cash at end of the year	2,835,132	434,503	688,702	1,275,844
Supplemental schedule of cash flow information
Interest paid	3,031	465	95
Non-cash activities
Settlement of amount due from a related party through repurchase of ordinary shares (Note 16)	2,559	392
Payable related to the IPO issuance cost	9,684	1,484
Payables for purchase of property and equipment	13,024	1,996	4,096	216
Right-of-use assets obtained in exchange for operating lease obligations	169,725	26,011	56,448	30,110
Exercise of warrant (Note 9)	1,014	155
Reconciliation to amounts on the Consolidated Balance Sheets
Cash and cash equivalents	2,834,962	434,477	653,859	1,252,983
Restricted cash	170	26	34,843	22,861
Total cash, cash equivalents and restricted cash	2,835,132	434,503	¥ 688,702	¥ 1,275,844
Series F Convertible Redeemable Preferred Shares
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from the issuance of convertible redeemable preferred shares	¥ 849,528	$ 130,196

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)
Statement Of Cash Flows [Abstract]
Redeemable preferred shares net of issuance cost	¥ 15,770

Organization and Principal Acti

Organization and Principal Activities	12 Months Ended
Organization and Principal Activities	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Principal Activities	1. ORGANIZATION AND PRINCIPAL ACTIVITIES 17 Education & Technology Group Inc. (the "Company"), was incorporated under the laws of the Cayman Islands on October 30, 2012. The Company, its subsidiaries, its consolidated variable interest entities ("VIEs") and VIEs' subsidiaries (collectively the "Group") are primarily engaged in providing K-12 online education service in the People's Republic of China ("PRC"). As of December 31, 2020, the Company's major subsidiary and VIE were as follows: Name ( 1) Later of date of establishment or acquisition Place of establishment Percentage of direct or indirect economic ownership Principal activities Subsidiary: Shanghai Yiqi Zuoye Information Technology Co., Ltd. ("Shanghai WFOE") April 23, 2013 PRC 100% Education services VIE: Shanghai Hexu Information Technology Co., Ltd ("Shanghai VIE") December 03, 2012 PRC 100% Education services (1) The English names are for identification purpose only.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of presentation and use of estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). These accounting principles require management to make certain estimates and assumptions that affect the amounts in the accompanying financial statements. Actual results may differ from those estimates. The Group bases its estimates on past experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Significant accounting estimates reflected in the Group's financial statements include, but are not limited to, consolidation of VIEs, revenue recognition, valuation allowance for deferred tax assets, useful lives of property and equipment, valuation of share-based compensation, and valuation of ordinary shares and preferred shares. Actual results may differ materially from those estimates. Principles of consolidation The accompanying consolidated financial statements include the financial information of the Company and its subsidiaries, the VIEs and the VIEs' subsidiaries. All intercompany balances and transactions were eliminated upon consolidation. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements In order to comply with the PRC laws and regulations which prohibit or restrict foreign control of companies involved in provision of value-added telecommunication services and other restricted businesses, the Company operates substantially all of its business through its VIEs. The Company through its wholly owned subsidiaries (the “WFOE”) located in the PRC entered into a series of contractual agreements with the VIEs and their shareholders. Through below contractual agreements, the Company has (1) the power to direct the activities that most significantly affect the economic performance of the VIEs, and (2) the right to receive the economic benefit of the VIEs that could potentially be significant to the VIEs. As a result, the shareholders of the VIEs lack the power to direct the activities of the VIEs that most significantly impact the entity's economic performance, the obligation to absorb the expected losses, and the right to receive the expected residual returns of the entity. Accordingly, the Company is considered as the primary beneficiary of the VIEs, and the Company has consolidated the financial results of the VIEs and their subsidiaries in its consolidated financial statements. As of December 31, 2020, the Group's VIE that is material to the Group’s business and operations is Shanghai Hexu Information Technology Co., Ltd. Exclusive Management Services and Business Cooperation Agreement Pursuant to the exclusive management services and business cooperation agreement among the WFOE, the VIEs and the shareholders of the VIEs, the WFOE has the exclusive right to provide or designate any third party to provide, among other things, technical support and consultation services, client relationship building up services, perfection of management structure and strategic consultation services to the VIEs and their subsidiaries. In exchange, the VIEs and their subsidiaries pay service fees to the WFOE at an amount determined by the WFOE in its sole discretion and can be adjusted by the WFOE unilaterally. Without the prior written consent of the WFOE, the VIEs are prohibited from engaging any third party to provide any services contemplated by this agreement and can neither dispose any important asset in any way nor change the equity structure on its self. The agreement has an initial term of ten years and shall automatically renew at the end of each term for a further term of ten years, unless otherwise terminated by the WFOE in its sole discretion with 10 days' prior written notice. Equity Interest Pledge Agreement Under the equity interest pledge agreement among the WFOE, the VIEs and the VIEs' shareholders, the VIEs' shareholders pledged all of their equity of the VIEs to the WFOE as security for performance of the obligations of the VIEs and VIEs' shareholders and their spouses, as applicable, under the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney and consent letters. If any of the specified events of default occurs, the WFOE can exercise the right as pledgee to enforce the pledge by, among other ways, auction or sale of the pledged equity interests. The equity interest pledge agreement will remain in effect until the earlier of (i) the fulfillment of all the obligations under the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney, and consent letters, (ii) the exercise of right of pledge by the WFOE pursuant to the terms and conditions of the equity interest pledge agreement, or (iii) that the shareholders of VIEs transfer all the equity held in VIEs to the WFOE or its designee(s) pursuant to the exclusive call option agreement. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Exclusive Call Option Agreement Under the exclusive call option agreement among the WFOE, the VIEs and the VIEs' shareholders, each of the shareholders of the VIEs irrevocably granted the WFOE a right to purchase or designated third party to purchase equity interests in the VIEs at a purchase price of RMB1.0 or equal to the lowest price permissible by the PRC laws and regulations. If the purchase price is higher than RMB1.0, the shareholders of the VIEs shall promptly give all considerations they received from the exercise of the options to the WFOE or its designee(s). The VIEs and their shareholders covenanted that, without the WFOE's prior written consent, they will not, among other things, (i) transfer or otherwise dispose of their equity interests in the VIEs; (ii) create any pledge or any other third party's right on their equity interests in the VIEs; (iii) change the VIEs' registered capital or merge the VIEs with other entities; (iv) dispose or force the management to dispose any material assets of the VIEs, except for the disposal of the assets that are treated as necessary for the VIEs' daily business operations; (v) cause the VIEs to terminate or force the management to terminate any material contracts to which the VIEs is a party; (vi) appoint or replace any director, supervisor or management of the VIEs; (vii) declare or distribute dividends; (viii) terminate, liquidate or dissolve the VIEs; (ix) amend the VIEs' articles of association; (x) allow the VIEs to incur any debts, or any other form of liabilities other than the liabilities incurred for usual course of business operation; (xi) lend funds or provide guarantee to third party in any form. The agreement has an initial term of ten years and shall automatically renew at the end of each term for a further term of ten years, unless otherwise terminated by WFOE in its sole discretion with 10 days’ prior written notice. Under no circumstances can VIEs or their shareholders terminate the exclusive call option agreement. Proxy Agreement and Powers of Attorney Pursuant to the proxy agreement and powers of attorney executed by the VIEs' shareholders, each of them irrevocably authorized the WFOE to act on their respective behalf as exclusive agent and attorney, to the extent permitted by law, with respect to all rights of shareholders concerning all the equity interest and sponsor interest held by each of them in the VIEs or their subsidiaries, including but not limited to proposing to convene or attend shareholder meeting, exercising all the rights as shareholders (including but not limited to voting rights, nomination rights, appointment rights, the right to sell or transfer of all the equity interest held in part or in whole). The agreement will remain effective within the operating period of VIEs, unless otherwise unilaterally terminated by the WFOE in its sole discretion. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Consent Letters Pursuant to the consent letters executed by each shareholder of the VIEs and their spouse, each signing shareholder and their spouses has confirmed and agreed to the execution of the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney, and the equity interest pledge agreement described above by the applicable shareholders. They further undertook not to hinder the disposal of the equity and not to make any assertions in connection with the equity of the VIEs held by the applicable shareholders, and confirmed that the applicable shareholders can perform the relevant transaction documents described above and further amend or terminate such transaction documents without the authorization or consent from such spouses. The spouse of each applicable shareholder agreed and undertook that if they obtain any equity of the VIE held by the applicable shareholder for any reasons, she would be bound by the transaction documents described above. Risks in relation to VIE structure The Company believes that the contractual arrangements with the VIEs and VIE's shareholders are in compliance with existing PRC laws and regulations and are legally enforceable. However, the contractual arrangements are subject to risks and uncertainties, including: The VIEs and VIE's shareholders may have or develop interests that conflict with the Group's interests, which may lead them to pursue opportunities in violation of the aforementioned contractual agreements. If the Group cannot resolve any conflicts of interest or disputes between the Group and the shareholders of the VIE, the Group would have to rely on legal proceedings, which could result in disruption of its business, and there is substantial uncertainty as to the outcome of any such legal proceedings. The VIEs and VIE's shareholders could fail to obtain the proper operating licenses or fail to comply with other regulatory requirements. As a result, the PRC government could impose fines, new requirements or other penalties on the VIEs or the Group, mandate a change in ownership structure or operations for the VIEs or the Group, restrict the VIEs or the Group's use of financing sources or otherwise restrict the VIE or the Group's ability to conduct business. The PRC government may declare the aforementioned contractual arrangements invalid. They may modify the relevant regulations, have a different interpretation of such regulations, or otherwise determine that the Group or the VIE have failed to comply with the legal obligations required to effectuate such contractual arrangements. If the legal structure and contractual arrangements were found to be in violation of PRC laws and regulations, the PRC government may restrict or prohibit the Group's business and operations in China. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Risks in relation to VIE structure - continued The Group's ability to conduct its business may be negatively affected if the PRC government were to carry out any of the aforementioned actions. As a result, the Group may not be able to consolidate the VIEs and VIEs' subsidiaries in the consolidated financial statements as the Group may lose the ability to exert effective control over the VIEs and VIEs' shareholders, and the Group may lose the ability to receive economic benefits from the VIEs. The Group's business has been directly operated by the VIEs and their subsidiaries. As of December 31, 2019 and 2020, the VIEs and VIEs' subsidiaries accounted for an aggregate of 34% and 24% of the Group's consolidated total assets, respectively, and 61% and 67% of the Group's consolidated total liabilities, respectively. The following financial information of the Company's VIEs and VIEs' subsidiaries after the elimination of inter-company transactions and balances as of December 31, 2019 and 2020 and for the years ended December 31, 2018, 2019 and 2020 was included in the accompanying consolidated financial statements: As of December 31, 2019 2020 RMB RMB Cash and cash equivalents 142,502 419,970 Restricted cash 24,653 170 Prepaid expenses and other current assets 43,628 175,002 Total current assets 210,783 595,142 Property and equipment, net 41,486 80,919 Right-of-use asset 53,875 110,939 Other non-current assets 9,804 30,475 Total non-current assets 105,165 222,333 Total assets 315,948 817,475 Short-term borrowings 9,000 - Accrued expenses and other current liabilities 151,413 213,481 Deferred revenue, current 224,092 571,827 Operating lease liabilities, current 28,179 46,835 Total current liabilities 412,684 832,143 Operating lease liabilities, non-current 18,325 56,427 Deferred revenue, non-current 652 1,982 Total non-current liabilities 18,977 58,409 Total liabilities 431,661 890,552 Year ended December 31, 2018 2019 2020 RMB RMB RMB Net revenues 97,009 362,282 1,229,126 Net (loss) income (45,056 ) (99,973 ) 301,096 Net cash generated from operating activities 31,728 159,753 347,773 Net cash used in investing activities (7,126 ) (38,396 ) (85,788 ) Net cash generated from (used in) financing activities — 9,000 (9,000 ) 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Risks in relation to VIE structure - continued There are no consolidated VIEs' assets that are collateral for the VIEs' obligations and which can only be used to settle the VIEs' obligations as of December 31, 2020. No creditors (or beneficial interest holders) of the VIEs have recourse to the general credit of the Company or any of its consolidated subsidiaries. No terms in any arrangements, considering both explicit arrangements and implicit variable interests, require the Company or its subsidiaries to provide financial support to the VIEs. However, if the VIEs ever needs financial support, the Company or its subsidiaries may, at its option and subject to statutory limits and restrictions, provide financial support to the VIEs through loans to the shareholders of the VIEs or entrustment loans to the VIEs. Foreign currency translation and transactions The Group's reporting currency is Renminbi ("RMB"). The functional currency of the subsidiaries incorporated outside the mainland China is United States dollar ("US dollar" or "US$"). The functional currency of all the other subsidiaries, the VIEs and VIEs' subsidiaries is RMB. Monetary assets and liabilities denominated in currencies other than the applicable functional currencies are translated into the functional currencies at the prevailing rates of exchange at the balance sheet date. Nonmonetary assets and liabilities are remeasured into the applicable functional currencies at historical exchange rates. Revenues and expenses are translated using the average rate of exchange in effect during the reporting period. Translation adjustments are reported and shown as a separate component of other comprehensive loss in the consolidated statements of changes in shareholders' deficit and the consolidated statements of comprehensive loss. Transactions in currencies other than the functional currencies during the year are converted into the applicable functional currencies at the applicable rates of exchange prevailing at the dates of the transactions. Transaction gains and losses are recorded in the consolidated statements of operations. Convenience translation The Group's business is primarily conducted in China and all of the revenues are denominated in RMB. However, periodic reports made to shareholders will include current period amounts translated into US dollars using the exchange rate as of balance sheet date, for the convenience of the readers. Translations of balances in the consolidated balance sheets and the related consolidated statements of operations, comprehensive loss, change in shareholders' deficit and cash flows from Renminbi ("RMB") into US dollars as of and for the year ended December 31, 2020 are solely for the convenience of the readers and were calculated at the rate of US$1.00=RMB6.5250 representing the noon buying rate set forth in the H.10 statistical release of the U.S. Federal Reserve Board on December 31, 2020. No representation is made that the RMB amounts could have been, or could be, converted, realized or settled into US$ at that rate on December 31, 2020, or at any other rate. Cash and cash equivalents Cash and cash equivalents comprise cash at banks and on hand, which have original maturities of three months or less when purchased and are subject to insignificant risk of changes in value. Restricted cash Restricted cash primarily consists of deposits in specific bank accounts held as guarantees in connection with short-term borrowings and notes payable processing. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Fair value Fair value is considered to be the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required or permitted to be recorded at fair value, the Group considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability. Authoritative literature provides a fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The level in the hierarchy within which the fair value measurement in its entirety falls is based upon the lowest level of input that is significant to the fair value measurement as follows: Level 1 applies to assets or liabilities for which there are quoted prices in active markets for identical assets or liabilities. Level 2 applies to assets or liabilities for which there are inputs other than quoted prices included within Level 1 that are observable for the asset or liability such as quoted prices for similar assets or liabilities in active markets; quoted prices for identical assets or liabilities in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. Level 3 applies to assets or liabilities for which there are unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of the assets or liabilities. Financial instruments The Group's financial instruments consist primarily of cash and cash equivalents, restricted cash, receivables from third party payment platforms, amounts due from a related party, short-term borrowings and warrant liabilities. As of December 31, 2019 and 2020, the carrying values of cash and cash equivalents, restricted cash, receivable from third party payment platforms, amount due from a related party and short-term borrowings approximated their fair values reported in the consolidated balance sheets due to the short term maturities of these instruments. Warrant liabilities was recorded at fair value as of December 31, 2019. Property and equipment, net Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets, as follows: Category Estimated useful life Electronic equipment 3 to 5 years Leasehold improvement Shorter of the lease term or estimated economic life Software 3 to 5 years Furniture and office equipment 5 years Repair and maintenance costs are charged to expense as incurred, whereas the cost of renewals and betterment that extends the useful lives of property and equipment are capitalized as additions to the related assets. Retirements, sales and disposals of assets are recorded by removing the cost and accumulated depreciation from the assets and accumulated depreciation accounts with any resulting gain or loss reflected in the consolidated statements of operations. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Impairment of long-lived assets The Group reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may no longer be recoverable. When these events occur, the Group measures impairment by comparing the carrying value of the long-lived assets to the estimated undiscounted future cash flows expected to result from the use of the assets and their eventual disposition. If the sum of the expected undiscounted cash flow is less than the carrying amount of the assets, the Group would recognize an impairment loss based on the fair value of the assets. The Group did not record any impairment loss on its long-lived assets during the years ended December 31, 2018, 2019 and 2020. Revenue recognition In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers ("Topic 606"). This standard replaces existing revenue recognition rules with a comprehensive revenue measurement and recognition standard and expanded disclosure requirements. The Group has adopted the new standard as of January 1, 2018 using the full retrospective method which requires the Group to present its financial statements for all periods as if Topic 606 had been applied to all prior periods. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Group's revenue is reported net of discount, value added tax and related surcharges. Prior to 2019, the revenue of the Group was primarily generated from self-directed learning resource subscription services. The Group began to provide K-12 online tutoring services in 2017, which subsequently became a major revenue stream in 2019. The primary sources of the Group's revenues are as follows: (1) Online K-12 tutoring services The Group offers various types of online K-12 tutoring services. The Group's online K-12 tutoring services consist of several components, including online live broadcasting classes, provisioning of teaching material, academic assessment and evaluation of learning outcomes during the period. Different service components are highly interdependent and interrelated in the context of the contract with the live interactive tutoring services because the service components are all designed specifically for each class and would not be able to fulfill the service promise if transferred independently to the customers. Therefore, the Group has determined that the live interactive tutoring services represent one performance obligation. The service period for the live interactive tutoring services is generally less than four months. The Group also offers the customers a content playback service once each of the live tutoring class is delivered. In the content playback service, the customers have unlimited access to recorded audio-video content of the previous live tutoring classes for three years. No other interactions or activities are provided during the playback period. The Group determined that the live interactive tutoring service and content playback service are two separate performance obligations under Topic 606, as these two deliverables are distinct customers can benefit from each other on their own and the Group's promises to deliver the services are separately identifiable from each other in the contract. Tutoring fees are collected in advance. The Group determines that there is not a significant financing component based on the nature of the service being offered and the purpose of the payment terms. Students are offered a full, unconditional refund if students withdraw 30 minutes before the start of the third class. The Group also offers refunds for any remaining undelivered classes to students who withdraw from the courses. The refund is equal to the amount related to the undelivered classes. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Revenue recognition - continued (1) Online K-12 tutoring services - continued The Group, from time to time, provides incentives to customers. The Group distributes cash coupons to attract both existing and prospective students to enroll in future classes. The students can redeem the cash coupons as a reduction to the payment for future online K-12 tutoring services. The coupon does not constitute material right as it is granted independently to the purchase of a course with the Group and is accounted for as a reduction of transaction price when the coupons are redeemed. The Group determines the transaction price to be earned by estimating the refund liability based on historical refund ratio on a portfolio basis using the expected value method, and allocates the tutoring fee excluding the estimate for refund liability to each performance obligation using the relative stand-alone selling price. The Group determines the stand-alone selling prices for live interactive tutoring services and content playback service using an expected cost plus margin methodology. Revenue related to the live interactive tutoring service is recognized proportionately as the online classes are delivered, as the Group concluded that the delivery of each online class represents a faithful depiction of when the services are provided to the students. Revenue related to the right to access the content playback is recognized proportionally over the playback period, as the Group concluded that the content playback service represents a stand ready obligation to provide the playback services and the customer simultaneously receives and consumes the benefits as the Group provides such services throughout the playback period. The revenue related to the content playback service is not material. (2) Other educational services Net revenues from other educational services in 2018 consisted primarily of the fees the Group charged for the self-directed learning resource subscription services. The Group ceased to provide these offerings in the second half of 2018. Net revenues from other educational services in 2019 and 2020 consisted primarily of the subscription fees the Group charged for its membership-based premium educational content, with a subscription periods ranging from 15 days to one year. The Group has determined that the self-directed learning resource subscription services and membership-based premium educational content subscription services each represent a performance obligation. The Group collects the content subscription fee in advance and records it as deferred revenue. Refunds are offered for the remaining undelivered services, which is accounted for as variable consideration similar to the online K-12 tutoring service business. Revenue is recognized ratably over the contract period as the Group concluded that the subscription services represent a stand ready obligation to provide the services while the member simultaneously receives and consumes the benefits of such services throughout the contract period. Contract and refund liabilities The following table provides information about the Group's contract and refund liabilities arising from contract with customers. The increase in contract liabilities primarily resulted from the Group's business growth. As of December 31, 2019 2020 RMB RMB Deferred revenue-current 243,521 596,307 Deferred revenue-non current 652 1,982 Refund liabilities 5,907 22,869 Deferred revenue primarily consists of tuition fees received from customers for which the Group's revenue recognition criteria have not been met. The deferred revenue will be recognized as revenue once related service are delivered. For the years ended December 31, 2019 and 2020, revenue recognized that was included in the deferred revenue balance at January 1, 2019 and January 1, 2020 amounted to RMB75,737 and RMB243,521, respectively. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Revenue recognition - continued Contract and refund liabilities - continued Refund liabilities represent the tutoring fee collected by the Group which it expects to refund back to its customer as a result of its refund policy. Refund liabilities are estimated based on the historical refund ratio for each type of courses provided. The Group's remaining performance obligations represents the amount of the transaction price for which service has not been performed. As of December 31, 2020, the aggregate amount of the transaction price allocated for the remaining performance obligations amounted to RMB598,289. The Group expects to recognize revenue of RMB596,307 and RMB1,342 related the remaining performance obligations over the next 12 months and 24 months, with the remainder of RMB640 recognized thereafter. The Group elected to apply the practical expedient to expense incremental costs of obtaining a contract when incurred as the amortization period of the contract cost that the Group otherwise would have amortized is generally less than one year. Disaggregation of revenue For the years ended December 31, 2018, 2019 and 2020, all of the Group's revenues were generated in the PRC. Additionally, all the revenues for the period were recognized from contracts with customers. The following table provides information about disaggregated revenue by types: Year ended December 31, 2018 2019 2020 RMB RMB RMB Online K-12 tutoring services 93,883 359,568 1,218,564 Other educational services 216,823 46,677 75,807 Total net revenues 310,706 406,245 1,294,371 Cost of Revenue Cost of revenues mainly consists of salaries, welfare and service fees for instructors and tutors, rental expenses for office space, depreciation and amortization of property and equipment, teaching materials and bandwidth costs. The compensations for instructors consist of base salary, as well as teaching fees based on hourly rates and the numbers of students enrolled in connection with courses delivered. The compensation of tutors consists of base salary and performance-based compensation, which is determined based on student retention and exercise completion. The Group accrues on a monthly basis for the cost of tutors which includes base salary, compensation for exercise marking as well as student retention bonus. The retention bonus is estimated by using the expected number of successful recurring course purchase, multiplied by the bonus rate. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Research and development expenses Research and development expenses primarily consist of (i) salaries and benefits for development of course content, product and technology development personnel, and (ii) office rental, general expenses and depreciation expenses associated with the research and development activities. The Group's research and development activities primarily consist of the development and enhancement of the Group's educational content, applications and platforms. The Group has expensed all research and development expenses when incurred. Sales and marketing expenses Sales and marketing expenses primarily consist of (i) teaching materials and gifts provided for promotional online courses, (ii) salaries, benefits and commission for sales and marketing personnel, (iii) office rental, general expenses and depreciation and amortization expenses associated with the sales and marketing activities. The Group expenses advertising costs as incurred. Total advertising costs incurred were RMB5,788, RMB2,644 and RMB163,768 for the years ended December 31, 2018, 2019 and 2020, respectively. Value added taxes ("VAT") The Group's services are subject to VAT at the rate of 3% for small-scale-VAT-payer entities or at the rate of 6% for general-VAT-payer entities in accordance with relevant PRC tax rules. Leases The Group leases offices in different cities in the PRC under operating leases. The Group determines whether an arrangement constitutes a lease at inception and records lease liabilities and right-of-use assets on its consolidated balance sheets at the lease commencement. The Group measures its lease liabilities based on the present value of the total lease payment

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
Prepaid Expenses and Other Current Assets	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid Expense and Other Current Assets	3 . PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following: As of December 31, 2019 2020 RMB RMB Prepaid VAT 21,430 71,418 Prepaid other service fees ( 1) 18,252 54,128 Prepaid advertising expenses - 52,114 Deposits 1,767 11,217 Receivables from third party payment platforms (2) 11,274 7,402 Prepaid rental expenses ( 3) 10,665 6,606 Others 2,923 8,563 66,311 211,448 (1) Prepaid other service fees mainly consisted of the prepayments for the purchase of promotion gifts, learning materials and the prepayments for third-party educational content subscription fee. The nature of such prepayment is generally short-term. (2) Receivables from third-party payment platforms consisted of cash that had been received from customers but held by the third-party payment platforms. The Group subsequently collected the full balances from the third-party payment platforms. (3) The prepaid rental expenses balance represented the prepaid rental expenses for short-term leases.

Property and Equipment,Net

Property and Equipment,Net	12 Months Ended
Property and Equipment,Net	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment,Net	4. PROPERTY AND EQUIPMENT, NET Property and equipment consisted of the following: As of December 31, 2019 2020 RMB RMB Electronic equipment 71,778 127,650 Leasehold improvement 35,171 47,988 Software 10,416 18,683 Furniture and office equipment 5,967 7,980 Total 123,332 202,301 Less: accumulated depreciation (58,163 ) (97,078 ) 65,169 105,223 Depreciation expenses were RMB15,760, RMB22,675 and RMB39,700 for the years ended December 31, 2018, 2019 and 2020, respectively.

Operating Leases

Operating Leases	12 Months Ended
Operating Leases	Dec. 31, 2020
Leases Operating [Abstract]
Operating Leases	5 OPERATING LEASES The Group's leases consist of operating leases for administrative office located in different cities in the PRC. Certain leases include rental escalation clauses with fixed rate rent increase over the term of the lease, which is factored into the Group’s determination of lease payments. As of December 31, 2019 and 2020, the Group has no finance lease. The components of lease expense for the years ended December 31, 2018, 2019 and 2020 were as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Operating lease cost 23,357 45,339 72,020 Lease cost for leases with terms less than one year 3,183 10,451 26,684 Total lease cost 26,540 55,790 98,704 For the years ended December 31, 2018, 2019 and 2020, there is no variable lease cost and sublease income recognized in the consolidated financial statements of the Group. The following is a maturity analysis as of December 31, 2019 and 2020: As of December 31, 2019 2020 RMB RMB 2020 45,937 - 2021 17,114 81,421 2022 6,708 69,726 2023 790 38,476 2024 - 14,807 2025 - 7,176 Less: imputed interest (6,115 ) (24,090 ) Total 64,434 187,516 The following table provides a summary of the Group's lease terms and discount rates for the years ended December 31, 2018, 2019 and 2020: Year ended December 31, 2018 2019 2020 Weighted average remaining lease term (years) 2.14 1.88 3.04 Weighted average discount rate (percentage) 4.94 6.29 8.58 Supplemental information related to the Group's operating leases for the years ended December 31, 2018, 2019 and 2020 were as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Cash paid for operating leases 29,995 46,990 70,458

Other Non-current Assets

Other Non-current Assets	12 Months Ended
Other Non-current Assets	Dec. 31, 2020
Other Assets Noncurrent [Abstract]
Other Non-current Assets	6 . OTHER NON-CURRENT ASSETS Other non-current assets consisted of the followings: As of December 31, 2019 2020 RMB RMB Prepayment for purchase of property and equipment 1,636 19,799 Rental deposits 12,278 13,875 Others 2,945 4,108 16,859 37,782

Short-term Borrowings

Short-term Borrowings	12 Months Ended
Short-term Borrowings	Dec. 31, 2020
Short Term Borrowings [Abstract]
Short-term Borrowings	7 . SHORT-TERM BORROWINGS Short-term borrowings consisted of the followings: As of December 31, 2019 2020 RMB RMB Bank Borrowings 85,000 - (1) In December 2019, one PRC subsidiary of the Group entered into a facility agreement with a PRC commercial bank (the "Lender") to obtain a short-term borrowing facility totalling RMB67,000, which is guaranteed by the Hong Kong subsidiary of the Group and the Company. In December 2019, a loan of RMB67,000 under this facility was drawn, bearing a fixed interest rate of one year Loan Prime Rate plus 2.35% per annum. The loan was fully repaid in July 2020. According to the facility agreement, the Company issued a warrant to a designee of the Lender that is measured at fair value at the end of each period. The amount of the warrant is insignificant. (2) In October and November 2019, a VIE and a subsidiary of the Group entered into two one-year bank loan agreements with another PRC commercial bank. Each borrowed loan amounted to RMB9,000 with fixed interest rates of 4.35%. The loans were pledged with the restricted term deposits with the total amount of RMB20,000. The loans were fully repaid in 2020. The use of proceeds of short-term borrowings are for general corporate operation purposes. The carrying amount of short-term borrowings approximates their fair value as the interest rates are at the same level of current market yield for comparable debts and the original maturities are short-term.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
Accrued Expenses and Other Current Liabilities	Dec. 31, 2020
Accrued Liabilities And Other Liabilities [Abstract]
Accrued Expenses and Other Current Liabilities	8 . ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES The components of accrued expenses and other current liabilities were as follows: As of December 31, 2019 2020 RMB RMB Salary and welfare payable 124,191 215,551 Accrued expenses for paid and promotional courses (1) 91,319 141,163 Accrued operating expenses (2) 61,331 133,096 Refund liabilities (3) 5,907 22,869 Payable for acquisitions of property and equipment 4,096 13,024 Payable related to the IPO issuance cost - 9,684 Other tax payable 6,641 4,400 Notes payable to suppliers (4) 13,698 - Warrant liabilities 1,848 - 309,031 539,787 (1) Accrued expenses for paid and promotional courses represented accrued expenses for online K-12 tutoring services, mainly teaching material and human resource service fee to third-party service providers. (2) Accrued operating expenses mainly represented free gifts to users of in-school products, technical support expenses and other operating expenses. (3) Refund liabilities represented the estimated amounts of service fee received that is estimated to be refunded as described in Note 2. (4) Notes payable to suppliers represented the payables in relation to the production of learning materials

Fair Value Measurement

Fair Value Measurement	12 Months Ended
Fair Value Measurement	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurement	9. FAIR VALUE MEASUREMENT Measured at fair value on a recurring basis The Group measured warrant liabilities at fair value as of December 31, 2019. Fair Value Measurement at Reporting Date Using Description Fair value as of December 31, 2019 Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) RMB RMB RMB RMB Warrant liabilities 1,848 - - 1,848 Total 1,848 - - 1,848 The warrants were exercised upon the completion of the IPO in December 2020.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
Share-Based Compensation	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	10 . On March 9, 2015, the Group adopted the 2015 Share Option Plan ("2015 Plan"), under which the maximum number of shares that may be granted is 59,899,375 shares. The vesting schedules ranged from two to five years with the options vesting on various dates during the vesting periods. 2018 Share Option Plan On January 12, 2018, the Group adopted the 2018 Share Option Plan ("2018 Plan"), under which 2020 Share Incentive Plan On November 12, 2020, the Group adopted the 2020 Share Incentive Plan ("2020 Plan"), under The vesting schedules under the 2020 Plan shall be determined by the plan administrator, which is specified in the relevant award agreements. As of December 31, 2020, the Group had granted 5,130,305 restricted share units under the 2020 Plan to the Founder. Number of options Weighted average exercise price Weighted average remaining contract life Weighted average grant date fair value Aggregate intrinsic value US$ US$ US$ Outstanding as of January 1, 2020 69,721,006 0.90 6.62 0.53 44,616,903 Granted** 16,969,200 0.21 3.49 Forfeited (3,661,874 ) 1.40 1.02 Repurchased and cancelled (30,000 ) 0.0014* 0.10 Exercised (6,052,167 ) 0.0014* 0.18 Cancelled (replaced by restricted shares) (32,855,200 ) 0.0014* 1.55 Outstanding as of December 31, 2020 44,090,965 0.19 5.62 0.91 217,347,100 Vested and expect to vest as of December 31, 2020 44,090,965 0.19 5.62 0.91 217,347,100 Exercisable as of December 31, 2020 31,864,055 0.27 4.40 0.39 154,713,978 ** 1,315,000 options were granted with performance conditions. The Company recognized the compensation cost during the year ended December 31, 2020, for which it became probable that the performance target will be achieved. The Group reassessed the probability of achieving the performance target at the end of each reporting period and would record a cumulative catch-up adjustment for any changes to its assessment. 1 0 . SHARE-BASED COMPENSATION - continued As noted below, for the year ended December 31, 2020, 46,568,242 options were modified. As a result, weighted average exercise prices decreased from US$0.90 per share as of December 31, 2019 to US$0.19 per share as of December 31, 2020. In determining the fair value of the share options, the binomial option pricing model was applied. The key assumptions used to determine the fair value of the options at the respective grant dates in 2018, 2019 and 2020 were as follows: For the years ended December 31, Grant date 2018 2019 2020 Expected volatility 48.3%~50.5% 50.1%~50.8% 50.1%~50.9% Risk-free interest rate 3.7%~3.9% 3.2%~3.3% 2.7%~3.2% Exercise multiples 2.2~2.8 2.2~2.8 2.2~2.8 Expected dividend yield 0.0% 0.0% 0.0% Life of options 10 years 10 years 10 years Fair value of underlying ordinary shares $1.31~$1.48 $1.32~$1.52 $1.52~$4.20 (1) Expected volatility The volatility of the underlying ordinary shares during the lives of the options was estimated based on the historical stock price volatility of comparable listed companies over a period comparable to the expected term of the options. (2) Risk-free interest rate Risk-free interest rate was estimated based on the daily treasury long term rate of the U.S. Treasury Department with a maturity period close to the expected term of the options, plus the country default spread of China. (3) Exercise multiples Exercise multiple represents the value of the underlying share as a multiple of exercise price of the option which, if achieved, results in exercise of the option. (4) Dividend yield The dividend yield was estimated by the Group based on its expected dividend policy over the expected term of the options. (5) Life of options Life of options was extracted from option agreements. (6) Fair value of underlying ordinary shares Prior to the IPO, the estimated fair value of the ordinary shares underlying the options as of the respective grant dates was determined based on a valuation with the assistance of a third party appraiser. After the completion of the IPO in December 2020, the fair value of the underlying ordinary shares is determined based on the closing market price of the share. 1 0 . SHARE-BASED COMPENSATION - continued Repurchase of vested options During 2018, 2019 and 2020, the Company voluntarily repurchased employees' vested options upon the termination of their employment in cash. Those options were subsequently cancelled. Cash payments amounting to RMB23,948, RMB1,355 and RMB528 were made during the years ended December 31, 2018, 2019 and 2020, respectively. The Group recorded the cash payment made amounting to the fair value of the vested option repurchased at the repurchase date directly to equity. The Group recorded any excess of the repurchase price over the fair value of the vested options repurchased as additional compensation cost. Modification of options In March 2020, the Company’s board of directors approved to modify certain terms for all outstanding options granted to employees of the Group as of March 2020. Upon entering into the amended option agreement, the exercise price of all the options was decreased to US$0.0014 per share. The vesting schedules of all those options remained unchanged. The Company accounted for this as a modification, resulting a total incremental cost of RMB239,044. In addition to the decrease of the exercise price, the exercisability of certain of those options was also modified such that certain of those options will not be exercisable until 180 days after the completion of an IPO. This change resulted in a probable to improbable (Type II) modification as the IPO was a performance condition that the Company anticipated would not be satisfied until occurrence. Accordingly, the incremental cost related to those options, amounting to RMB84,648 was not be recognized unless and until the performance condition becomes probable. The Company continues to recognize compensation cost equal to the award’s original grant-date fair value when the original vesting conditions are satisfied, regardless of whether the modified IPO condition is met. Upon the completion of the IPO in December 2020, the Company recorded compensation expense amounting to RMB48,683 related to this modification. For the remaining options, the total incremental cost as a result of the modification amounted to RMB154,396. RMB39,766 was recognized on the date of modification, and the remaining is recognized ratably over the remaining vesting period of the award. Employee Benefit Trust In June 2020, the Company established 17 Prosperity Trust, a company controlled by the Company as a vehicle to hold shares that will be used to provide incentives and rewards to management team members who contribute to the success of the Company’s operations (the "Shareholding Platform"). The Shareholding Platform has no activities other than administrating the incentive programs and does not have any employees. On behalf of the Company and subject to approvals from its board of directors, an advisory committee was set up in the Shareholding Platform, who holds the authority and responsibility to process the eligible participants to whom awards will be granted, the number of shares, the terms and conditions of such awards. 1 0 . SHARE-BASED COMPENSATION - continued Employee Benefit Trust - continued In June and October 2020, the Group granted 32,855,200 restricted shares to certain management (the "Selected Management") to replace options previously granted under the 2015 and 2018 plan. The purchase price of the restricted shares of US$0.0014 per share is the exercised price of the original options and was paid by the Selected Management at the time the restricted shares were granted. The vesting and other requirements imposed on the restricted shares were the same as those under the original option granted. As a result, the Group accounted for the issuance of restricted shares in exchange of the options of the Selected Management as a modification. Incremental compensation expense as a result of this modification was immaterial. The restricted shares received by the Selected Management were immediately transferred to the Shareholding Platform. All shareholder rights of the nonvested restricted shares, including but not limited to voting rights and dividend rights, are unconditionally waived until the shares are vested. As a result, all nonvested shares held by the Shareholding Platform are solely for purpose of future issuance to employees once they vest, and have been treated as treasury shares in the consolidated financial statements. The following table summarized the Group’s activities of restricted shares held by the Shareholding Platform for the year ended December 31, 2020: Number of Restricted Shares Grant date fair value per share US$ Outstanding as of January 1, 2020 - - Granted (to replace existing options) 32,855,200 3.0 Vested (14,326,831 ) 2.7 Cancelled - - Outstanding as of December 31, 2020 18,528,369 3.2 The share-based compensation expenses recognized for these restricted shares held by the Shareholding Platform for the years ended December 31, 2018, 2019 and 2020, were nil, nil and RMB44,625, respectively. 1 0 . SHARE-BASED COMPENSATION - continued Employee Benefit Trust - continued As of December 31, 2020, the unrecognized compensation expense related to the restricted shares held by the Shareholding Platform amounted to RMB331,840, which will be recognized over a weighted-average period of 3.38 years. Restricted shares to Mr. Andy Chang LIU, the founder, chairman and Chief Executive Officer of the Group (the "Founder") (1) As one of the conditions to the closing of the Series D Preferred Shares, the Company entered into a restricted share purchase agreement with the Founder. Pursuant to this agreement, the Company issued an aggregate 25,449,238 ordinary shares at a par value of $0.0001. 17,920,282 shares were issued to replace the same amount of nonvested options previously granted in 2014, which were cancelled in full. The remaining 7,528,956 shares were newly granted. The Company has the option to repurchase the ordinary shares held by the Founder at par value of the ordinary shares in the event of voluntary or involuntary termination of employment of the Founder (the "Repurchase Right"). The Repurchase Right functions as a forfeiture provision. The restricted share ("the Repurchase Right Restricted Shares") are released from the Company's Repurchase Right over 48 equal monthly installments starting from the grant date. Additionally, in accordance with the restricted share purchase agreement, all restricted shares granted to the Founder will be released from the Repurchase Right and other restrictions upon the earlier of (i) a qualified public offering of the Company, (ii) a trade sale of the Company pursuant to which the equity valuation of the Company immediately prior to such trade sale being not less than $1,200,000, or (iii) the completion of any equity financing of the Company from any third party pursuant to which the pre-money equity valuation of the Company immediately prior to the completion of such financing is not less than $1,200,000. The Founder is entitled to cash dividend on the nonvested restricted shares. The Company accounted for the above transaction as a modification and measured the fair value of the restricted shares of the Founder at the grant date. The Company recognized any unrecognized compensation cost remaining from the original nonvested shares as well as any incremental cost at the time of the modification over the remaining portion of the modified award. The Company assessed the occurrence of the acceleration conditions described in the preceding paragraph and concluded that those were not probable to occur during the 4 years following the date of grant. As such, the Company recognizes the compensation expense over the service period of 4 years since the date of grant. (2) On January 12, 2018, in connection with the issuance of Series E convertible redeemable preferred shares, the Company granted an aggregate 12,851,801 nonvested restricted shares to the Founder with a par value of $0.0001. The nonvested restricted shares vest in three equal installments on the closing date of the issuance of Series E convertible redeemable preferred shares, the first anniversary and the second anniversary of the closing date. If an IPO of the Company occurs prior to first or second anniversary of the closing date, any ordinary shares not then issued will be fully issued to the Founder immediately prior to the completion of the IPO. The nonvested restricted shares have no voting and dividend rights. On January 16, 2019, the Founder waived his right to receive the third installment shares amounting to 4,283,934. The Company accounted for the above as a cancellation of the award. Any remaining unrecognized compensation cost, amounting to RMB42,910, was recognized at the cancellation date. 10 . SHARE-BASED COMPENSATION - continued Restricted shares to Mr. Any Chang LIU, the founder, chairman and Chief Executive Officer of the Group (the "Founder") - continued (3) In November 2020, the Group granted 5,130,305 restricted share units under the 2020 Plan to Number of Restricted Shares Grant date fair value per share US$ Outstanding as of January 1, 2020 - - Granted 5,130,305 4.20 Vested (5,130,305 ) 4.20 Cancelled - - Outstanding as of December 31, 2020 - - Total share-based compensation expenses recognized for the restricted shares and restricted share units held by the Founder As of In September 2020, the Founder and Mr. Dun XIAO, the co-founder and the director of the Group Total share-based compensation expense of share options and restricted shares recognized for the years ended December 31, 2018, 2019 and 2020 were as follows: For the years ended December 31 2018 2019 2020 RMB RMB RMB Sales and marketing expenses 4,911 8,737 35,077 Research and development expenses 12,254 22,508 68,688 General and administrative expenses 106,365 61,845 252,273 123,530 93,090 356,038

Convertible Redeemable Preferre

Convertible Redeemable Preferred Shares	12 Months Ended
Convertible Redeemable Preferred Shares	Dec. 31, 2020
Temporary Equity Disclosure [Abstract]
Convertible Redeemable Preferred Shares	11. CONVERTIBLE REDEEMABLE PREFERRED SHARES In January 2018, the Company issued 78,824,567 Series E convertible redeemable preferred shares with an issue price of US$3.1716 per share to a group of investors for a total consideration of RMB1,603,837 (equivalent to US$250,000). In June 2020, the Company issued 33,186,759 Series F convertible redeemable preferred shares with an issue price of US$3.6159 per share to an investor for a total consideration of RMB849,528 (equivalent to US$120,000). The key terms of the Series B, Series B+, Series C, Series D, Series E and Series F convertible redeemable preferred shares are summarized as follows: 11. CONVERTIBLE REDEEMABLE PREFERRED SHARES - continued Conversion Each holder of convertible redeemable preferred shares shall have the right, at such holder's sole discretion, to convert all or any portion of the preferred shares into ordinary shares on a one-for-one basis at any time. The initial conversion price is the issuance price of preferred shares, subject to adjustment in the event of (1) share dividends, subdivisions, combinations or consolidation of ordinary shares, (2) reclassification, exchange and substitution, and (3) issuance of new securities at a price per share less than the applicable conversion price in effect on the date of and immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance. Each preferred share shall automatically be converted into ordinary shares, based on the then applicable conversion price for each convertible redeemable preferred share, without the payment of any additional consideration, into fully-paid and non-assessable ordinary shares upon (i) the closing of the Qualified IPO as defined below, or (ii) the written consent of (A) the holders holding a majority of the then outstanding Series B convertible redeemable preferred shares, or (B) written consent of the requisite holders holding Series B+ convertible redeemable preferred shares, or (C) written consent of the holders holding at least eighty percent (80%) of the then outstanding Series C convertible redeemable preferred shares, or (D) written consent of the requisite holders holding Series D convertible redeemable preferred shares, or (E) written consent of the requisite holders holding Series E convertible redeemable preferred shares, or (F) written consent of the requisite holders holding Series F convertible redeemable preferred shares. Qualified IPO is defined as a public offering of the ordinary shares of the Company on the Nasdaq Global Market System, the Main Board or the Growth Enterprise Market of the Hong Kong Stock Exchange, or any other recognized regional or national securities exchange acceptable to the requisite preferred shares holders, with an offering price (exclusive of underwriting commissions and expenses) that reflects the equity valuation of the Company immediately prior to such offering being not less than US$2,000,000 and the gross proceeds to be received by the Company from which public offering are not less than US$100,000, as amended upon the issuance of Series F convertible redeemable preferred shares. Redemption The holders of convertible redeemable preferred shares shall have the right to redeem if the Qualified IPO has not been consummated by the 48th month from the Series F convertible redeemable preferred shares original issue date, the Company shall redeem, out of funds legally available, ( i ) all but not less than all of the issued and outstanding Series F convertible redeemable preferred shares at the request of holders of a majority vote of outstanding Series F convertible redeemable preferred shares, voting as a separate class, at the applicable redemption price; (ii) all but not less than all of the issued and outstanding Series E convertible redeemable preferred shares at the request of holders of a majority vote of outstanding Series E convertible redeemable preferred shares, voting as a separate class, at the applicable redemption price; (iii) all but not less than all of the issued and outstanding Series D convertible redeemable preferred shares upon the affirmative consent of requisite Series D investors, at the applicable redemption price; 11. CONVERTIBLE REDEEMABLE PREFERRED SHARES - continued Redemption - continued (iv) all but not less than all of the issued and outstanding Series C convertible redeemable preferred shares at the request of holders of a majority vote of outstanding Series C convertible redeemable preferred shares, voting as a separate class, at the applicable redemption price; and/or (v) all but not less than all of the issued and outstanding Series B convertible redeemable preferred shares and Series B+ In the case of events with material adverse effect occurred, the Company shall, at any time, at the request of any holder of Series D convertible redeemable preferred shares or any holder of Series E convertible redeemable preferred shares or any holder of Series F convertible redeemable preferred shares, redeem, out of funds legally available therefore including capital, all but not less than all of the issued and outstanding Series D convertible redeemable preferred shares or Series E convertible redeemable preferred shares or Series F convertible redeemable preferred shares held by such investors. The applicable redemption price per share is equal to the greater of ( i ) the amount of one hundred percent (100%) of the applicable Series B issue price, one hundred percent (100%) of the applicable Series B+ issue price, one hundred percent (100%) of the applicable Series C issue price, one hundred percent (100%) of the applicable Series D issue price, one hundred percent (100%) of the applicable Series E issue price, one hundred percent (100%) of the applicable Series F issue price with an fifteen percent (15%) compound per annum return (if the period is less than one year, such return shall be calculated pro rata) calculating from the applicable Series B issue date, Series B+ issue date, Series C issue date, Series D issue date, Series E issue date, or Series F issue date (as the case may be) to the redemption price payment date, plus any accrued but unpaid dividends thereon up to the date of redemption, and (ii) the fair market value of such class of convertible redeemable preferred shares, the valuation of which shall be determined through an independent appraisal performed by a reputable appraisal firm mutually agreed upon by the holder of a majority of the such class of convertible redeemable preferred shares (voting as a separate class and on an as-converted basis) and the Company; provided that such valuation shall not take into account any liquidity or minority interest discounts. 11. CONVERTIBLE REDEEMABLE PREFERRED SHARES - continued Liquidation Preference In the event of any liquidation, dissolution or winding up of the Company, either voluntary or involuntary, distributions shall be made in the following manner (after satisfaction of all creditors' claims and claims that may be preferred by law): ( i ) The holders of Series A convertible preferred shares (Note 13), Series B/B+ convertible redeemable preferred shares, Series C convertible redeemable preferred shares, Series D convertible redeemable preferred shares, Series E convertible redeemable preferred shares and Series F convertible redeemable preferred shares (collectively "Preferred Shares") shall be entitled to receive the amount equal to 100% of their respective issue prices, plus all declared but unpaid dividends on such Preferred Shares. The liquidation preference is exercised in the sequence of Series F convertible redeemable preferred shares, Series E convertible redeemable preferred shares, Series D convertible redeemable preferred shares, Series C convertible redeemable preferred shares, Series B/B+ convertible redeemable preferred shares and Series A convertible preferred shares. (ii) If there are any assets or funds remaining after distribution in full to the holders of Preferred Shares, the remaining assets and funds of the Group that is legally available for distribution to the shareholders shall be distributed to the holders of the Preferred Shares and ordinary shares ratably amongst them in proportion to the number of ordinary shares held by them on an as-converted basis. Dividends ( i ) Each holder of convertible redeemable preferred shares shall be entitled to receive noncumulative dividend at the rate of eight percent (8%) of the applicable Series B issue price, Series B+ issue price, Series C issue price, Series D issue price, Series E issue price or Series F issue price as the case may be, per annum for each such share held by such holder, payable out of funds or assets when and as such funds or assets become legally available therefore on parity with each other, prior and in preference to, and satisfied before, any dividend on any other class or series of shares. Such dividends shall be payable only when, as, and if declared by the Board of Directors. (ii) No dividend or distribution, whether in cash, in property, or in any other shares of the Group, shall be declared, paid, set aside or made with respect to the ordinary shares at any time unless all accrued but unpaid dividends on the convertible redeemable preferred shares set forth in term (i), if any, have been paid in full, and a distribution is likewise declared, paid, set aside or made, respectively, at the same time with respect to each outstanding convertible redeemable preferred shares such that the dividend or distribution declared, paid, set aside or made to the holder thereof shall be equal to the dividend or distribution that such holder would have received pursuant to this term if such convertible redeemable preferred shares had been converted into ordinary shares immediately prior to the record date for such dividend or distribution, or if no such record date is established, the date such dividend or distribution is made, and if such share then participated in and the holder thereof received such dividend or distribution. 11. CONVERTIBLE REDEEMABLE PREFERRED SHARES - continued Voting Rights Subject to the provisions of Sixth Amended and Restated Memorandum and Articles (including any Article providing for special voting rights), at all general meetings of the Group: (a) the holder of each ordinary share issued and outstanding shall have one vote in respect of each ordinary share held, and (b) the holder of Preferred Shares shall be entitled to such number of votes as equals the whole number of ordinary share into which such holder's collective Preferred Shares are convertible immediately after the close of business on the record date of the determination of the Group's members entitled to vote or, if no such record date is established, at the date such vote is taken or any written consent of the Group's members is solicited, to the extent that the statute or the articles allow the Preferred Shares to vote separately as a class or series with respect to any matters, the Preferred Shares, shall have the right to vote separately as a class or series with respect to such matters. Accounting for the Convertible Redeemable Preferred Shares The Group has classified the convertible redeemable preferred shares as mezzanine equity as these preferred shares are redeemable upon the occurrence of an event not solely within the control of the Group. In addition, the Group accretes changes in the redemption value of the convertible redeemable preferred shares based on the higher of (i) the subscription price plus a pre-determined compounded annualized return set forth in the agreement and (ii) fair market value. The change in redemption value is recorded against retained earnings, or in the absence of retained earnings, against additional paid-in capital. Once additional paid-in capital has been exhausted, additional charges are recorded by increasing the accumulated deficit. The Group has determined that there was no beneficial conversion feature attributable to all preferred shares because the initial effective conversion price of these preferred shares was higher than the fair value of the Group's common shares determined by the Group taking into account independent valuations. The following table summarized the roll forward of the carrying amount of the convertible redeemable preferred shares for the years ended December 31, 2018, 2019 and 2020: Series B Series B+ Series C Series D Series E Series F Total RMB RMB RMB RMB RMB RMB RMB January 1, 2018 322,238 503,116 488,780 928,472 - - 2,242,606 Issuance - - - - 1,588,067 - 1,588,067 Accretion (32,313 ) (50,491 ) (44,257 ) 139,272 232,160 - 244,371 December 31, 2018 289,925 452,625 444,523 1,067,744 1,820,227 - 4,075,044 Issuance - - - - - - - Accretion 40,892 63,844 60,198 160,161 275,440 - 600,535 December 31, 2019 330,817 516,469 504,721 1,227,905 2,095,667 - 4,675,579 Issuance - - - - - 849,528 849,528 Accretion 559,428 873,734 804,702 170,197 292,699 137,231 2,837,991 Conversion (890,245 ) (1,390,203 ) (1,309,423 ) (1,398,102 ) (2,388,366 ) (986,759 ) (8,363,098 ) December 31, 2020 - - - - - - - 11. CONVERTIBLE REDEEMABLE PREFERRED SHARES - continued Accounting for the Convertible Redeemable Preferred Shares - continued As of December 31, 2020, a summary of convertible redeemable preferred shares is as follows: Series Average Issue Price Per Share Issue Date Shares Issued Shares outstanding as of January 1, 2019 and 2020 Issuance of convertible redeemable preferred shares Conversion of the convertible redeemable preferred shares upon the IPO Shares outstanding as of December 31, 2020 Proceeds from issuance, net of issuance cost Carrying Amount as of December 31, 2020 US$ RMB RMB B 0.1738 06/06/2013 34,815,112 34,544,762 - (34,544,762 ) - 37,122 - B+ 0.1849 09/06/2013 54,083,288 54,083,288 - (54,083,288 ) - 61,202 - C 0.3586 04/12/2014 50,195,203 50,195,203 - (50,195,203 ) - 111,800 - D 1.9923 03/09/2015 50,193,243 50,193,243 - (50,193,243 ) - 626,350 - E 3.1716 01/12/2018 78,824,567 78,824,567 - (78,824,567 ) - 1,588,067 - F 3.6159 06/26/2020 33,186,759 - 33,186,759 (33,186,759 ) - 849,528 - 301,298,172 267,841,063 33,186,759 (301,027,822 ) - 3,274,069 - Upon the completion of the IPO, all of the Company’s Preferred Shares were converted into Class A Ordinary shares on an one-to-one basis except for the 3,305,651 Series E convertible redeemable preferred shares held by the Founder, which were converted into Class B Ordinary shares on an one-to-one basis.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	12. INCOME TAXES Cayman Islands The Company is a tax-exempted company incorporated in Cayman Islands. Under the current laws of Cayman Islands, the Company is not subject to income, corporate or capital gains tax, and Cayman Islands currently have no form of estate duty, inheritance tax or gift tax. In addition, payments of dividends and capital in respect of their shares are not subject to taxation and no withholding will be required in the Cayman Islands on the payment of any dividend or capital to any holder of their shares, nor will gains derived from the disposal of their shares be subject to Cayman Islands income or corporation tax. No provision for income taxes in Cayman Islands has been made as the Company had no taxable income for the years ended December 31, 2018, 2019 and 2020. Hong Kong The Company's subsidiary, Sunny Education (HK) Limited is located in Hong Kong and is subject to an income tax rate of 8.25% for assessable profit up to HKD2,000,000 from April 2018 onwards, and an income tax rate of 16.5% on any part of assessable profits over HKD2,000,000. No provision for Hong Kong profits tax was made as the Group had no estimated assessable profit that was subject to Hong Kong profits tax during 2018, 2019 and 2020. PRC The Company's subsidiary, the VIEs and the VIEs' subsidiaries, which were entities incorporated in the PRC (the "PRC entities"), are subject to PRC Enterprise Income Tax ("EIT") on their taxable income in accordance with the relevant PRC income tax laws, which have adopted a unified income tax rate of 25% since January 1, 2008. Shanghai VIE qualified as a High and New Technology Enterprise from 2016 to 2022 and accordingly was entitled to the 15% preferential tax rate during the period. The income tax expenses in the consolidated statements of operations were nil, nil and nil for the years ended December 31, 2018, 2019 and 2020, respectively. 12. INCOME TAXES – continued PRC - continued The principal components of deferred taxes were as follows: As of December 31, 2018 2019 2020 RMB RMB RMB Deferred tax assets Accrued expenses 7,242 9,231 12,142 Advertising expenses carrying forwards - - 24,202 Depreciation of property and equipment 1,318 853 388 Net operating loss carrying forwards 295,682 503,212 724,597 Total deferred tax assets 304,242 513,296 761,329 Less: valuation allowance (304,242 ) (513,296 ) (761,329 ) Deferred tax assets, net - - - As of December 31, 2020, the Group had net operating loss carried forward of RMB3,056,123 from the Group's PRC entities, which will expire on various dates from December 31, 2021 to December 31, 2030. The reconciliation of the effective tax rate and the statutory income tax rate applicable to PRC operations was as follow: Year ended December 31, 2018 2019 2020 RMB RMB RMB Loss before provision for income taxes (656,071 ) (963,750 ) (1,339,908 ) Income tax benefit computed at an applicable tax rate of 25% (164,018 ) (240,938 ) (334,977 ) Effect of non-deductible expenses 2,821 3,738 11,540 Effect of research and development expenses super deduction (2,361 ) (10,740 ) (24,037 ) Effect of preferential tax rate 6,988 18,413 18,513 Effect on tax rates in different tax jurisdictions 30,113 20,473 80,928 Change in valuation allowance 126,457 209,054 248,033 - - - If the tax holidays granted to Shanghai VIE were not available, there would be no income tax expenses incurred for the Group and no impact on the basic and diluted net loss per ordinary share attributable to the Company, for the three years ended December 31, 2020. 12. INCOME TAXES - continued PRC - continued The movements of valuation allowance for the years end December 31, 2018, 2019 and 2020 are as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Balance at beginning of the period 177,785 304,242 513,296 Additions 126,457 209,054 248,033 Reversal - - - Balance at end of the period 304,242 513,296 761,329 The Group did not identify significant unrecognized tax benefits for the years ended December 31, 2018, 2019 and 2020. The authoritative guidance requires that the Group recognizes the impact of a tax position in the financial statements if that position is more likely than not of being sustained upon audit by the tax authority, based on the technical merits of the position. Under PRC laws and regulations, arrangements and transactions among related parties may be subject to examination by the PRC tax authorities. If the PRC tax authorities determine that the contractual arrangements among related companies do not represent a price under normal commercial terms, they may make adjustments to the companies' income and expenses. A transfer pricing adjustment could result in additional tax liabilities. The Group did not have any significant unrecognized uncertain tax positions as of and for the years ended December 31, 2018, 2019 and 2020. In addition, uncertainties exist with respect to how the current income tax law in the PRC applies to the Group's overall operations, and more specifically, with regard to tax residency status. The New Enterprise Income Tax ("EIT") Law includes a provision specifying that legal entities organized outside of the PRC will be considered residents for Chinese income tax purposes if the place of effective management or control is within the PRC. The implementation rules to the New EIT Law provide that non-resident legal entities will be considered PRC residents if substantial and overall management and control over the manufacturing and business operations, personnel, accounting and properties, occurs within the PRC. Despite the present uncertainties resulting from the limited PRC tax guidance on the issue, the Group does not believe that the legal entities organized outside of the PRC within the Group should be treated as residents for EIT law purposes. If the PRC tax authorities subsequently determine that the Company and its subsidiaries registered outside the PRC should be deemed resident enterprises, the Company and its subsidiaries registered outside the PRC will be subject to the PRC income taxes, at a rate of 25%.

Ordinary Shares and Series A Co

Ordinary Shares and Series A Convertible Preferred Shares	12 Months Ended
Ordinary Shares and Series A Convertible Preferred Shares	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Ordinary Shares and Series A Convertible Preferred Shares	13. ORDINARY SHARES AND SERIES A CONVERTIBLE PREFERRED SHARES Ordinary shares The Company’s Amended and Restated Memorandum of Association authorizes the Company to issue 509,631,372 ordinary shares with a par value of US$0.0001 per share as of December 31, 2019. As of December 31, 2019, the Company had 57,864,058 ordinary shares issued and outstanding. In December 2020, the Company completed its IPO and issued 31,510,000 ADSs (representing 78,775,000 Class A ordinary shares). The net proceeds raised from the IPO and from exercising the over-allotment option by the underwriters were RMB2,023,593, net of issuance cost of RMB28,153. Upon the completion of the IPO, 77,884,733 ordinary shares outstanding then were re-designated to 27,867,521 Class A ordinary shares and 50,017,212 Class B ordinary shares. Holders of Class A ordinary shares and Class B ordinary shares have the same rights except for voting and conversion rights. Each Class A ordinary share is entitled to one vote, and each Class B ordinary share is entitled to thirty votes and is convertible into one Class A ordinary share. Class A ordinary shares are not convertible into Class B ordinary shares under any circumstances. Series A Convertible Preferred Shares Series A convertible preferred shares are not redeemable but convertible to ordinary shares at an one-for-one initial conversion ratio at the option of the holders at any time after the date of issuance or automatically be converted upon the closing of the Qualified IPO at the applicable conversion price. The liquidation preference of Series A convertible preferred shares is preferable to ordinary shares but subordinated to convertible redeemable preferred shares as disclosed in Note 11. During 2017, the Company repurchased some ordinary shares and Series A convertible preferred shares from investors. Any cash paid in excess of the fair value of the shares at the time of repurchase was recorded as a deemed distribution during 2017. Additionally, the Company only completed the payments to the investors of the above repurchases in 2018. Upon the completion of the IPO, all Series A convertible preferred shares were converted into Class A Ordinary shares on an one-to-one basis.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
Net Loss Per Share	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	14. NET LOSS PER SHARE The following table sets forth the computation of basic and diluted net loss per share for the periods Year ended December 31, 2018 2019 2020 RMB RMB RMB Numerator: Net loss attributable to ordinary shareholders (900,442 ) (1,564,285 ) (4,177,899 ) Denominator: Weighted average ordinary shares outstanding used in computing basic and diluted net loss per share 48,676,298 57,410,827 93,503,437 Basic and diluted loss per share (18.50 ) (27.25 ) (44.68 ) 14. NET LOSS PER SHARE - continued For the years ended December 31, 2018, 2019 and 2020, the following shares outstanding were excluded from the calculation of diluted net loss per ordinary share, as their inclusion would have been anti-dilutive for the periods prescribed. Year ended December 31, 2018 2019 2020 Shares issuable upon exercise of share options 55,957,332 69,409,835 55,825,379 Shares issuable upon vesting of restricted shares 12,914,110 423,804 9,272,591 Shares issuable upon conversion of Series A convertible preferred shares 17,085,275 17,085,275 - Shares issuable upon conversion of Series B convertible redeemable preferred shares 34,544,762 34,544,762 - Shares issuable upon conversion of Series B+ convertible redeemable preferred shares 54,083,288 54,083,288 - Shares issuable upon conversion of Series C convertible redeemable preferred shares 50,195,203 50,195,203 - Shares issuable upon conversion of Series D convertible redeemable preferred shares 50,193,243 50,193,243 - Shares issuable upon conversion of Series E convertible redeemable preferred shares 76,449,032 78,824,567 - Warrants (Note 8) - 4,959 -

Employee Defined Contribution P

Employee Defined Contribution Plan	12 Months Ended
Employee Defined Contribution Plan	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Defined Contribution Plan	15. EMPLOYEE DEFINED CONTRIBUTION PLAN Full time employees of the Group in the PRC participate in a government mandated defined contribution plan, pursuant to which certain pension benefits, medical care, employee housing fund, unemployment insurance and other welfare benefits are provided to employees. Chinese labor regulations require that the Group's PRC entities make contributions to the government for these benefits based on certain percentages of the employees' salaries. The Group has no legal obligation for the benefits beyond the contributions made. The total amount for such employee benefits, which was expensed as incurred, was RMB99,720, RMB132,728 and RMB100,957 for the years ended December 31, 2018, 2019 and 2020, respectively.

Related Party Transaction

Related Party Transaction	12 Months Ended
Related Party Transaction	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transaction	16. RELATED PARTY TRANSACTION (1) Related party Name of related party Relationship with the Group Fluency Holding Ltd. Entity wholly owned by the Founder Mr. Dun XIAO Co-Founder and Director (2) As of December 31, 2019 2020 RMB RMB Amounts due from: Fluency Holding Ltd. 2,611 - Total 2,611 - The balance with the related party was an interest-free, unsecured loan. On June 30, 2020, the Company and the Founder entered into a supplemental agreement, through which the maturity date of this loan was extended to the earlier of June 30, 2021 or the date of a public filing of any registration statement relating to an IPO. Additionally, on September 30, 2020, Fluency Holding Ltd, an entity controlled by the Founder, the Company and the Founder entered into a share repurchase agreement under which the Company agreed to repurchase a total of 115,324 ordinary shares to settle the loan. The shares were repurchased on September 30, 2020 and were immediately cancelled. The difference between the fair value of the shares repurchased and the loan receivable balance was immaterial. (3) In June 2020, a VIE of the Group entered into a share transfer agreement with Mr. Dun XIAO to acquire 100% equity interest of an entity wholly owned by Mr. Dun XIAO with no substantial operation which included a loan receivable from Mr. Dun XIAO of RMB589 for a consideration of RMB1,000 which equals to the paid in capital of the acquired entity. Shortly after the acquisition, the Group and Mr. Dun XIAO agreed to waive the loan and reduced the amount due to Mr. Dun XIAO by the same amount. The remaining consideration of RMB411 was fully repaid in September 2020.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. COMMITMENTS AND CONTINGENCIES Operating lease commitment Upon the adoption of ASC 842 on January 1, 2018, future minimum lease payments for operating lease liabilities as of December 31, 2019 and 2020 are disclosed in Note 5. Contingencies From time to time, the Group is subject to legal proceedings and claims incidental to the conduct of its business. The Group accrues the liability when the loss is probable and reasonably estimable.

Segment Information

Segment Information	12 Months Ended
Segment Information	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information	18. SEGMENT INFORMATION Operating segments are defined as components of an enterprise engaging in businesses activities for which separate financial information is available that is regularly evaluated by the Group's chief operating decision makers ("CODM") in deciding how to allocate resources and assess performance. The Group's CODM has been identified as the Chief Executive Officer ("CEO"), who reviews consolidated results including revenue, gross profit and operating profit at a consolidated level only. The CODM reviews consolidated results including revenue, gross profit and operating profit at a consolidated level only and does not distinguish between services for the purpose of making decisions about resources allocation and performance assessment. As such, the Group concluded that it has one operating segment and one reporting segment. The Group operates solely in the PRC and all of the Group's long-lived assets are located in the PRC.

Restricted Net Assets

Restricted Net Assets	12 Months Ended
Restricted Net Assets	Dec. 31, 2020
Restricted Net Assets [Abstract]
Restricted Net Assets	19. RESTRICTED NET ASSETS Relevant PRC statutory laws and regulations permit payments of dividends by the Group's PRC subsidiaries only out of their retained earnings, if any, as determined in accordance with PRC accounting standards and regulations. The results of operations reflected in the financial statements prepared in accordance with U.S. GAAP differ from those reflected in the statutory financial statements of the Company's subsidiaries. In accordance with the Regulations on Enterprises with Foreign Investment of China and their articles of association, a foreign invested enterprise established in the PRC is required to provide certain statutory reserves, namely general reserve fund, the enterprise expansion fund and staff welfare and bonus fund which are appropriated from net profit as reported in the enterprise's PRC statutory accounts, which is included in retained earnings accounts in equity section of the consolidated balance sheets. A wholly-owned foreign invested enterprise is required to allocate at least 10% of its annual after-tax profit to the general reserve until such reserve reaches 50% of its respective registered capital based on the enterprise's PRC statutory accounts. Appropriations to the enterprise expansion fund and staff welfare and bonus fund are at the discretion of the board of directors for all foreign invested enterprises. The aforementioned reserves can only be used for specific purposes and are not distributable as cash dividends. If any PRC subsidiary incur debt on its own behalf in the future, the instruments governing the debt may restrict their ability to pay dividends or make other payments to the Group. Any limitation on the ability of the PRC subsidiaries to distribute dividends or other payments to their respective shareholders could materially and adversely limit the ability to grow, make investments or acquisitions that could be beneficial to pay dividends. Additionally, in accordance with the Company Law of the PRC, a domestic enterprise is required to provide statutory common reserve at least 10% of its annual after-tax profit until such reserve reaches 50% of its respective registered capital based on the enterprise's PRC statutory accounts. The Group's provision for the statutory common reserve is in compliance with the aforementioned requirement of the Company Law. A domestic enterprise is also required to provide for discretionary surplus reserve, at the discretion of the board of directors, from the profits determined in accordance with the enterprise's PRC statutory accounts. The aforementioned reserves can only be used for specific purposes and are not distributable as cash dividends. Because the Group's entities in the PRC can only be paid out of distributable profits reported in accordance with PRC accounting standards, the Group's entities in the PRC are restricted from transferring a portion of their net assets to the Company. The restricted amounts include the paid-in capital and statutory reserves of the Group's entities in the PRC. The aggregate amount of paid-in capital and statutory reserves, which is the amount of net assets of the Group's entities in the PRC (mainland) not available for distribution, were RMB1,602,510 and RMB2,632,554, as of December 31, 2019 and 2020, respectively.

Additional Information Financia

Additional Information Financial Statement Schedule I	12 Months Ended
Additional Information Financial Statement Schedule I	Dec. 31, 2020
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Additional Information Financial Statement Schedule I	CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (In thousands of RMB and USD, except for share and per share data, or otherwise noted) As of December 31 2019 2020 2020 RMB RMB USD (Note 3) ASSETS Current assets Cash and cash equivalents 290,578 2,108,582 323,154 Amounts due from subsidiaries 771,355 716,696 109,838 Amounts due from a related party 2,611 - - Total current assets 1,064,544 2,825,278 432,992 TOTAL ASSETS 1,064,544 2,825,278 432,992 LIABILITIES, MEZZANINE EQUITY AND SHAREHOLDERS' (DEFICIT) EQUITY LIABILITIES Current liabilities Accrued expenses and other current liabilities 2,207 3,768 577 Total current liabilities 2,207 3,768 577 Non-current liabilities Deficits of investments in subsidiaries, VIEs and VIEs' subsidiaries 846,686 757,360 116,070 Total non-current liabilities 846,686 757,360 116,070 TOTAL LIABILITIES 848,893 761,128 116,647 MEZZANINE EQUITY Series B convertible redeemable preferred shares (US$0.0001 par value; 34,815,112 shares authorized as of December 31, 2019 and 2020, respectively, 34,544,762 shares issued and outstanding as of December 31, 2019 and 2020, respectively) 330,817 - - Series B+ convertible redeemable preferred shares (US$0.0001 par value; 54,083,288 shares authorized, issued and outstanding as of December 31, 2019 and 2020, respectively) 516,469 - - Series C convertible redeemable preferred shares (US$0.0001 par value; 50,195,203 shares authorized, issued and outstanding as of December 31, 2019 and 2020, respectively) 504,721 - - Series D convertible redeemable preferred shares (US$0.0001 par value; 50,193,243 shares authorized, issued and outstanding as of December 31, 2019 and 2020, respectively) 1,227,905 - - Series E convertible redeemable preferred shares (US$0.0001 par value; 78,824,567 shares authorized, issued and outstanding as of December 31, 2019 and 2020, respectively) 2,095,667 - - TOTAL MEZZANINE EQUITY 4,675,579 - - ADDITIONAL INFORMATION FINANCIAL STATEMENT SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (In thousands of RMB and USD, except for share and per share data, or otherwise noted) As of December 31 2019 2020 2020 RMB RMB USD (Note 3) SHAREHOLDERS' (DEFICIT) EQUITY Ordinary shares (par value of US$0.0001 per share; 509,631,372 and nil shares authorized as of December 31, 2019 and 2020, respectively, 57,864,058 shares and nil shares issued and outstanding as of December 31, 2019 and 2020, respectively) 37 - - Class A ordinary shares (par value of USD0.0001 per share; nil and 1,300,000,000 shares authorized as of December 31, 2019 and 2020, respectively; nil and 421,729,902 shares issued and outstanding as of December 31, 2019 and 2020, respectively) - 275 42 Class B ordinary shares (par value of USD0.0001 per share; nil and 100,000,000 shares authorized as of December 31, 2019 and 2020, respectively; nil and 58,453,168 shares issued and outstanding as of December 31, 2019 and 2020, respectively) - 38 6 Series A convertible preferred shares (US$0.0001 par value; 22,257,215 and nil shares authorized as of December 31, 2019 and 2020, respectively, 17,085,275 and nil issued and outstanding as of December 31, 2019 and 2020, respectively) 54,256 - - Additional paid-in capital - 10,653,403 1,632,705 Accumulated other comprehensive income 88,216 49,614 7,604 Accumulated deficit (4,602,437 ) (8,639,180 ) (1,324,012 ) TOTAL SHAREHOLDERS' (DEFICIT) EQUITY (4,459,928 ) 2,064,150 316,345 TOTAL LIABILITIES, MEZZANINE EQUITY AND TOTAL SHAREHOLDERS' (DEFICIT) EQUITY 1,064,544 2,825,278 432,992 ADDITIONAL INFORMATION FINANCIAL STATEMENT SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (In thousands of RMB and USD, except for share and per share data, or otherwise noted) Year ended December 31, 2018 2019 2020 2020 RMB RMB RMB USD (Note 3) Sales and marketing expenses (15,965 ) (8,737 ) (35,077 ) (5,376 ) Research and development expenses (12,254 ) (22,933 ) (68,688 ) (10,527 ) General and administrative expenses (115,253 ) (64,961 ) (257,873 ) (39,521 ) Total operating expenses (143,472 ) (96,631 ) (361,638 ) (55,424 ) Loss from operations (143,472 ) (96,631 ) (361,638 ) (55,424 ) Interest income 25,088 13,642 1,045 160 Foreign currency exchange (loss) gain (3,669 ) (779 ) 1,699 260 Loss before provision for income tax (122,053 ) (83,768 ) (358,894 ) (55,004 ) Income tax expenses - - - - Loss from investment in subsidiaries (534,018 ) (879,982 ) (981,014 ) (150,345 ) Net loss (656,071 ) (963,750 ) (1,339,908 ) (205,349 ) Accretion of convertible redeemable preferred shares (244,371 ) (600,535 ) (2,837,991 ) (434,941 ) Net loss available to ordinary shareholders of 17 Education & Technology Group Inc (900,442 ) (1,564,285 ) (4,177,899 ) (640,290 ) ADDITIONAL INFORMATION FINANCIAL STATEMENT SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (In thousands of RMB and USD, except for share and per share data, or otherwise noted) Year ended December 31, 2018 2019 2020 2020 RMB RMB RMB USD (Note 3) Net loss (656,071 ) (963,750 ) (1,339,908 ) (205,349 ) Other comprehensive income (loss), net of tax of nil: Change in cumulative foreign currency translation adjustments 69,566 (11,972 ) (38,602 ) (5,916 ) Total comprehensive loss (586,505 ) (975,722 ) (1,378,510 ) (211,265 ) ADDITIONAL INFORMATION FINANCIAL STATEMENT SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (In thousands of RMB and USD, except for share and per share data, or otherwise noted) Year ended December 31, 2018 2019 2020 2020 RMB RMB RMB USD (Note 3) Net cash generated from (used in) operating activities 1,477 11,529 (4,214 ) (646 ) CASH FLOWS FROM INVESTING ACTIVITIES: Amounts due from subsidiaries (142,237 ) (60,137 ) - - Investments in subsidiaries (539,608 ) (671,566 ) (1,024,607 ) (157,028 ) Net cash used in investing activities (681,845 ) (731,703 ) (1,024,607 ) (157,028 ) CASH FLOWS FROM FINANCING ACTIVITIES: Proceeds from the IPO and from exercising the over-allotment option by the underwriters - - 2,051,695 314,436 Payment of the IPO issuance cost - - (18,469 ) (2,830 ) Payment to repurchase ordinary shares (21,082 ) - - - Payment to repurchase of the Series A convertible preferred shares (4,730 ) - - - Repurchase and cancellation of vested options (11,883 ) (551 ) (528 ) (81 ) Net proceeds from the issuance of Series E convertible redeemable preferred shares (net of issuance cost of RMB15,770) 1,588,067 - - - Proceeds from issuance of Series F convertible redeemable preferred shares - - 849,528 130,196 Net cash generated from (used in) financing activities 1,550,372 (551 ) 2,882,226 441,721 Effect of exchange rate changes 114,770 (1,536 ) (35,401 ) (5,426 ) Net increase (decrease) in cash and cash equivalents 984,774 (722,261 ) 1,818,004 278,621 Cash and cash equivalents at beginning of the year 28,065 1,012,839 290,578 44,533 Cash and cash equivalents at end of the year 1,012,839 290,578 2,108,582 323,154 ADDITIONAL INFORMATION FINANCIAL STATEMENT SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY NOTES TO FINANCIAL STATEMENTS (In thousands of RMB and USD, except for share and per share data, or otherwise noted) 1. BASIS FOR PREPARATION The condensed financial information of the Parent Company has been prepared using the same accounting policies as set out in the Group's consolidated financial statements except that the Parent Company used the equity method to account for investments in its subsidiaries, VIEs and VIEs' subsidiaries. 2. INVESTMENT IN SUBSIDIARIES AND VIES AND VIES' SUBSIDIARIES The Parent Company and its subsidiaries, VIEs and VIEs' subsidiaries were included in the consolidated financial statements where inter-company balances and transactions were eliminated upon consolidation. For purpose of the Parent Company's stand-alone financial statements, its investments in subsidiaries, VIEs and VIEs' subsidiaries were reported using the equity method of accounting. The Parent Company's share of loss from its subsidiaries, VIEs and VIEs' subsidiaries were reported as share of loss of subsidiaries, VIEs and VIEs' subsidiaries in the accompanying Parent Company financial statements. Ordinarily under the equity method, an investor in an equity method investee would cease to recognize its share of the losses of an investee once the carrying value of the investment has been reduced to RMB nil absent an undertaking by the investor to provide continuing support and fund losses. For the purpose of this Schedule I, the Parent Company has continued to reflect its share, based on its proportionate interest, of the losses of subsidiaries, VIEs and VIEs' subsidiaries regardless of the carrying value of the investment even though the Parent Company is not obligated to provide continuing support or fund losses. 3. CONVENIENCE TRANSLATION The Group's business is primarily conducted in China and all of the revenues are denominated in RMB. However, periodic reports made to shareholders will include current period amounts translated into US dollars using the exchange rate as of balance sheet date, for the convenience of the readers. Translations of balances in the balance sheet, and the related statement of operations and cash flows from Renminbi ("RMB") into US dollars as of and for the year ended December 31, 2020 are solely for the convenience of the readers and were calculated at the rate of US$1.00=RMB6.5250, representing the noon buying rate set forth in the H.10 statistical release of the U.S. Federal Reserve Board on December 31, 2020. No representation is made that the RMB amounts could have been, or could be, converted, realized or settled into US$ at that rate on December 31, 2020, or at any other rate.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of presentation and use of estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). These accounting principles require management to make certain estimates and assumptions that affect the amounts in the accompanying financial statements. Actual results may differ from those estimates. The Group bases its estimates on past experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Significant accounting estimates reflected in the Group's financial statements include, but are not limited to, consolidation of VIEs, revenue recognition, valuation allowance for deferred tax assets, useful lives of property and equipment, valuation of share-based compensation, and valuation of ordinary shares and preferred shares. Actual results may differ materially from those estimates.
Principles of Consolidation	Principles of consolidation The accompanying consolidated financial statements include the financial information of the Company and its subsidiaries, the VIEs and the VIEs' subsidiaries. All intercompany balances and transactions were eliminated upon consolidation.
The VIE arrangements	The VIE arrangements In order to comply with the PRC laws and regulations which prohibit or restrict foreign control of companies involved in provision of value-added telecommunication services and other restricted businesses, the Company operates substantially all of its business through its VIEs. The Company through its wholly owned subsidiaries (the “WFOE”) located in the PRC entered into a series of contractual agreements with the VIEs and their shareholders. Through below contractual agreements, the Company has (1) the power to direct the activities that most significantly affect the economic performance of the VIEs, and (2) the right to receive the economic benefit of the VIEs that could potentially be significant to the VIEs. As a result, the shareholders of the VIEs lack the power to direct the activities of the VIEs that most significantly impact the entity's economic performance, the obligation to absorb the expected losses, and the right to receive the expected residual returns of the entity. Accordingly, the Company is considered as the primary beneficiary of the VIEs, and the Company has consolidated the financial results of the VIEs and their subsidiaries in its consolidated financial statements. As of December 31, 2020, the Group's VIE that is material to the Group’s business and operations is Shanghai Hexu Information Technology Co., Ltd. Exclusive Management Services and Business Cooperation Agreement Pursuant to the exclusive management services and business cooperation agreement among the WFOE, the VIEs and the shareholders of the VIEs, the WFOE has the exclusive right to provide or designate any third party to provide, among other things, technical support and consultation services, client relationship building up services, perfection of management structure and strategic consultation services to the VIEs and their subsidiaries. In exchange, the VIEs and their subsidiaries pay service fees to the WFOE at an amount determined by the WFOE in its sole discretion and can be adjusted by the WFOE unilaterally. Without the prior written consent of the WFOE, the VIEs are prohibited from engaging any third party to provide any services contemplated by this agreement and can neither dispose any important asset in any way nor change the equity structure on its self. The agreement has an initial term of ten years and shall automatically renew at the end of each term for a further term of ten years, unless otherwise terminated by the WFOE in its sole discretion with 10 days' prior written notice. Equity Interest Pledge Agreement Under the equity interest pledge agreement among the WFOE, the VIEs and the VIEs' shareholders, the VIEs' shareholders pledged all of their equity of the VIEs to the WFOE as security for performance of the obligations of the VIEs and VIEs' shareholders and their spouses, as applicable, under the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney and consent letters. If any of the specified events of default occurs, the WFOE can exercise the right as pledgee to enforce the pledge by, among other ways, auction or sale of the pledged equity interests. The equity interest pledge agreement will remain in effect until the earlier of (i) the fulfillment of all the obligations under the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney, and consent letters, (ii) the exercise of right of pledge by the WFOE pursuant to the terms and conditions of the equity interest pledge agreement, or (iii) that the shareholders of VIEs transfer all the equity held in VIEs to the WFOE or its designee(s) pursuant to the exclusive call option agreement. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Exclusive Call Option Agreement Under the exclusive call option agreement among the WFOE, the VIEs and the VIEs' shareholders, each of the shareholders of the VIEs irrevocably granted the WFOE a right to purchase or designated third party to purchase equity interests in the VIEs at a purchase price of RMB1.0 or equal to the lowest price permissible by the PRC laws and regulations. If the purchase price is higher than RMB1.0, the shareholders of the VIEs shall promptly give all considerations they received from the exercise of the options to the WFOE or its designee(s). The VIEs and their shareholders covenanted that, without the WFOE's prior written consent, they will not, among other things, (i) transfer or otherwise dispose of their equity interests in the VIEs; (ii) create any pledge or any other third party's right on their equity interests in the VIEs; (iii) change the VIEs' registered capital or merge the VIEs with other entities; (iv) dispose or force the management to dispose any material assets of the VIEs, except for the disposal of the assets that are treated as necessary for the VIEs' daily business operations; (v) cause the VIEs to terminate or force the management to terminate any material contracts to which the VIEs is a party; (vi) appoint or replace any director, supervisor or management of the VIEs; (vii) declare or distribute dividends; (viii) terminate, liquidate or dissolve the VIEs; (ix) amend the VIEs' articles of association; (x) allow the VIEs to incur any debts, or any other form of liabilities other than the liabilities incurred for usual course of business operation; (xi) lend funds or provide guarantee to third party in any form. The agreement has an initial term of ten years and shall automatically renew at the end of each term for a further term of ten years, unless otherwise terminated by WFOE in its sole discretion with 10 days’ prior written notice. Under no circumstances can VIEs or their shareholders terminate the exclusive call option agreement. Proxy Agreement and Powers of Attorney Pursuant to the proxy agreement and powers of attorney executed by the VIEs' shareholders, each of them irrevocably authorized the WFOE to act on their respective behalf as exclusive agent and attorney, to the extent permitted by law, with respect to all rights of shareholders concerning all the equity interest and sponsor interest held by each of them in the VIEs or their subsidiaries, including but not limited to proposing to convene or attend shareholder meeting, exercising all the rights as shareholders (including but not limited to voting rights, nomination rights, appointment rights, the right to sell or transfer of all the equity interest held in part or in whole). The agreement will remain effective within the operating period of VIEs, unless otherwise unilaterally terminated by the WFOE in its sole discretion. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Consent Letters Pursuant to the consent letters executed by each shareholder of the VIEs and their spouse, each signing shareholder and their spouses has confirmed and agreed to the execution of the exclusive call option agreement, the exclusive management services and business cooperation agreement, proxy agreement and powers of attorney, and the equity interest pledge agreement described above by the applicable shareholders. They further undertook not to hinder the disposal of the equity and not to make any assertions in connection with the equity of the VIEs held by the applicable shareholders, and confirmed that the applicable shareholders can perform the relevant transaction documents described above and further amend or terminate such transaction documents without the authorization or consent from such spouses. The spouse of each applicable shareholder agreed and undertook that if they obtain any equity of the VIE held by the applicable shareholder for any reasons, she would be bound by the transaction documents described above. Risks in relation to VIE structure The Company believes that the contractual arrangements with the VIEs and VIE's shareholders are in compliance with existing PRC laws and regulations and are legally enforceable. However, the contractual arrangements are subject to risks and uncertainties, including: The VIEs and VIE's shareholders may have or develop interests that conflict with the Group's interests, which may lead them to pursue opportunities in violation of the aforementioned contractual agreements. If the Group cannot resolve any conflicts of interest or disputes between the Group and the shareholders of the VIE, the Group would have to rely on legal proceedings, which could result in disruption of its business, and there is substantial uncertainty as to the outcome of any such legal proceedings. The VIEs and VIE's shareholders could fail to obtain the proper operating licenses or fail to comply with other regulatory requirements. As a result, the PRC government could impose fines, new requirements or other penalties on the VIEs or the Group, mandate a change in ownership structure or operations for the VIEs or the Group, restrict the VIEs or the Group's use of financing sources or otherwise restrict the VIE or the Group's ability to conduct business. The PRC government may declare the aforementioned contractual arrangements invalid. They may modify the relevant regulations, have a different interpretation of such regulations, or otherwise determine that the Group or the VIE have failed to comply with the legal obligations required to effectuate such contractual arrangements. If the legal structure and contractual arrangements were found to be in violation of PRC laws and regulations, the PRC government may restrict or prohibit the Group's business and operations in China. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Risks in relation to VIE structure - continued The Group's ability to conduct its business may be negatively affected if the PRC government were to carry out any of the aforementioned actions. As a result, the Group may not be able to consolidate the VIEs and VIEs' subsidiaries in the consolidated financial statements as the Group may lose the ability to exert effective control over the VIEs and VIEs' shareholders, and the Group may lose the ability to receive economic benefits from the VIEs. The Group's business has been directly operated by the VIEs and their subsidiaries. As of December 31, 2019 and 2020, the VIEs and VIEs' subsidiaries accounted for an aggregate of 34% and 24% of the Group's consolidated total assets, respectively, and 61% and 67% of the Group's consolidated total liabilities, respectively. The following financial information of the Company's VIEs and VIEs' subsidiaries after the elimination of inter-company transactions and balances as of December 31, 2019 and 2020 and for the years ended December 31, 2018, 2019 and 2020 was included in the accompanying consolidated financial statements: As of December 31, 2019 2020 RMB RMB Cash and cash equivalents 142,502 419,970 Restricted cash 24,653 170 Prepaid expenses and other current assets 43,628 175,002 Total current assets 210,783 595,142 Property and equipment, net 41,486 80,919 Right-of-use asset 53,875 110,939 Other non-current assets 9,804 30,475 Total non-current assets 105,165 222,333 Total assets 315,948 817,475 Short-term borrowings 9,000 - Accrued expenses and other current liabilities 151,413 213,481 Deferred revenue, current 224,092 571,827 Operating lease liabilities, current 28,179 46,835 Total current liabilities 412,684 832,143 Operating lease liabilities, non-current 18,325 56,427 Deferred revenue, non-current 652 1,982 Total non-current liabilities 18,977 58,409 Total liabilities 431,661 890,552 Year ended December 31, 2018 2019 2020 RMB RMB RMB Net revenues 97,009 362,282 1,229,126 Net (loss) income (45,056 ) (99,973 ) 301,096 Net cash generated from operating activities 31,728 159,753 347,773 Net cash used in investing activities (7,126 ) (38,396 ) (85,788 ) Net cash generated from (used in) financing activities — 9,000 (9,000 ) 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued The VIE arrangements - continued Risks in relation to VIE structure - continued There are no consolidated VIEs' assets that are collateral for the VIEs' obligations and which can only be used to settle the VIEs' obligations as of December 31, 2020. No creditors (or beneficial interest holders) of the VIEs have recourse to the general credit of the Company or any of its consolidated subsidiaries. No terms in any arrangements, considering both explicit arrangements and implicit variable interests, require the Company or its subsidiaries to provide financial support to the VIEs. However, if the VIEs ever needs financial support, the Company or its subsidiaries may, at its option and subject to statutory limits and restrictions, provide financial support to the VIEs through loans to the shareholders of the VIEs or entrustment loans to the VIEs.
Foreign Currency Translation and Transactions	Foreign currency translation and transactions The Group's reporting currency is Renminbi ("RMB"). The functional currency of the subsidiaries incorporated outside the mainland China is United States dollar ("US dollar" or "US$"). The functional currency of all the other subsidiaries, the VIEs and VIEs' subsidiaries is RMB. Monetary assets and liabilities denominated in currencies other than the applicable functional currencies are translated into the functional currencies at the prevailing rates of exchange at the balance sheet date. Nonmonetary assets and liabilities are remeasured into the applicable functional currencies at historical exchange rates. Revenues and expenses are translated using the average rate of exchange in effect during the reporting period. Translation adjustments are reported and shown as a separate component of other comprehensive loss in the consolidated statements of changes in shareholders' deficit and the consolidated statements of comprehensive loss. Transactions in currencies other than the functional currencies during the year are converted into the applicable functional currencies at the applicable rates of exchange prevailing at the dates of the transactions. Transaction gains and losses are recorded in the consolidated statements of operations.
Convenience Translation	Convenience translation The Group's business is primarily conducted in China and all of the revenues are denominated in RMB. However, periodic reports made to shareholders will include current period amounts translated into US dollars using the exchange rate as of balance sheet date, for the convenience of the readers. Translations of balances in the consolidated balance sheets and the related consolidated statements of operations, comprehensive loss, change in shareholders' deficit and cash flows from Renminbi ("RMB") into US dollars as of and for the year ended December 31, 2020 are solely for the convenience of the readers and were calculated at the rate of US$1.00=RMB6.5250 representing the noon buying rate set forth in the H.10 statistical release of the U.S. Federal Reserve Board on December 31, 2020. No representation is made that the RMB amounts could have been, or could be, converted, realized or settled into US$ at that rate on December 31, 2020, or at any other rate.
Cash and Cash Equivalents	Cash and cash equivalents Cash and cash equivalents comprise cash at banks and on hand, which have original maturities of three months or less when purchased and are subject to insignificant risk of changes in value.
Restricted Cash	Restricted cash Restricted cash primarily consists of deposits in specific bank accounts held as guarantees in connection with short-term borrowings and notes payable processing.
Fair Value	Fair value Fair value is considered to be the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required or permitted to be recorded at fair value, the Group considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability. Authoritative literature provides a fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The level in the hierarchy within which the fair value measurement in its entirety falls is based upon the lowest level of input that is significant to the fair value measurement as follows: Level 1 applies to assets or liabilities for which there are quoted prices in active markets for identical assets or liabilities. Level 2 applies to assets or liabilities for which there are inputs other than quoted prices included within Level 1 that are observable for the asset or liability such as quoted prices for similar assets or liabilities in active markets; quoted prices for identical assets or liabilities in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. Level 3 applies to assets or liabilities for which there are unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of the assets or liabilities.
Financial Instruments	Financial instruments The Group's financial instruments consist primarily of cash and cash equivalents, restricted cash, receivables from third party payment platforms, amounts due from a related party, short-term borrowings and warrant liabilities. As of December 31, 2019 and 2020, the carrying values of cash and cash equivalents, restricted cash, receivable from third party payment platforms, amount due from a related party and short-term borrowings approximated their fair values reported in the consolidated balance sheets due to the short term maturities of these instruments. Warrant liabilities was recorded at fair value as of December 31, 2019.
Property and Equipment, Net	Property and equipment, net Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets, as follows: Category Estimated useful life Electronic equipment 3 to 5 years Leasehold improvement Shorter of the lease term or estimated economic life Software 3 to 5 years Furniture and office equipment 5 years Repair and maintenance costs are charged to expense as incurred, whereas the cost of renewals and betterment that extends the useful lives of property and equipment are capitalized as additions to the related assets. Retirements, sales and disposals of assets are recorded by removing the cost and accumulated depreciation from the assets and accumulated depreciation accounts with any resulting gain or loss reflected in the consolidated statements of operations.
Impairment of Long-Lived Assets	Impairment of long-lived assets The Group reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may no longer be recoverable. When these events occur, the Group measures impairment by comparing the carrying value of the long-lived assets to the estimated undiscounted future cash flows expected to result from the use of the assets and their eventual disposition. If the sum of the expected undiscounted cash flow is less than the carrying amount of the assets, the Group would recognize an impairment loss based on the fair value of the assets. The Group did not record any impairment loss on its long-lived assets during the years ended December 31, 2018, 2019 and 2020.
Revenue Recognition	Revenue recognition In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers ("Topic 606"). This standard replaces existing revenue recognition rules with a comprehensive revenue measurement and recognition standard and expanded disclosure requirements. The Group has adopted the new standard as of January 1, 2018 using the full retrospective method which requires the Group to present its financial statements for all periods as if Topic 606 had been applied to all prior periods. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Group's revenue is reported net of discount, value added tax and related surcharges. Prior to 2019, the revenue of the Group was primarily generated from self-directed learning resource subscription services. The Group began to provide K-12 online tutoring services in 2017, which subsequently became a major revenue stream in 2019. The primary sources of the Group's revenues are as follows: (1) Online K-12 tutoring services The Group offers various types of online K-12 tutoring services. The Group's online K-12 tutoring services consist of several components, including online live broadcasting classes, provisioning of teaching material, academic assessment and evaluation of learning outcomes during the period. Different service components are highly interdependent and interrelated in the context of the contract with the live interactive tutoring services because the service components are all designed specifically for each class and would not be able to fulfill the service promise if transferred independently to the customers. Therefore, the Group has determined that the live interactive tutoring services represent one performance obligation. The service period for the live interactive tutoring services is generally less than four months. The Group also offers the customers a content playback service once each of the live tutoring class is delivered. In the content playback service, the customers have unlimited access to recorded audio-video content of the previous live tutoring classes for three years. No other interactions or activities are provided during the playback period. The Group determined that the live interactive tutoring service and content playback service are two separate performance obligations under Topic 606, as these two deliverables are distinct customers can benefit from each other on their own and the Group's promises to deliver the services are separately identifiable from each other in the contract. Tutoring fees are collected in advance. The Group determines that there is not a significant financing component based on the nature of the service being offered and the purpose of the payment terms. Students are offered a full, unconditional refund if students withdraw 30 minutes before the start of the third class. The Group also offers refunds for any remaining undelivered classes to students who withdraw from the courses. The refund is equal to the amount related to the undelivered classes. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Revenue recognition - continued (1) Online K-12 tutoring services - continued The Group, from time to time, provides incentives to customers. The Group distributes cash coupons to attract both existing and prospective students to enroll in future classes. The students can redeem the cash coupons as a reduction to the payment for future online K-12 tutoring services. The coupon does not constitute material right as it is granted independently to the purchase of a course with the Group and is accounted for as a reduction of transaction price when the coupons are redeemed. The Group determines the transaction price to be earned by estimating the refund liability based on historical refund ratio on a portfolio basis using the expected value method, and allocates the tutoring fee excluding the estimate for refund liability to each performance obligation using the relative stand-alone selling price. The Group determines the stand-alone selling prices for live interactive tutoring services and content playback service using an expected cost plus margin methodology. Revenue related to the live interactive tutoring service is recognized proportionately as the online classes are delivered, as the Group concluded that the delivery of each online class represents a faithful depiction of when the services are provided to the students. Revenue related to the right to access the content playback is recognized proportionally over the playback period, as the Group concluded that the content playback service represents a stand ready obligation to provide the playback services and the customer simultaneously receives and consumes the benefits as the Group provides such services throughout the playback period. The revenue related to the content playback service is not material. (2) Other educational services Net revenues from other educational services in 2018 consisted primarily of the fees the Group charged for the self-directed learning resource subscription services. The Group ceased to provide these offerings in the second half of 2018. Net revenues from other educational services in 2019 and 2020 consisted primarily of the subscription fees the Group charged for its membership-based premium educational content, with a subscription periods ranging from 15 days to one year. The Group has determined that the self-directed learning resource subscription services and membership-based premium educational content subscription services each represent a performance obligation. The Group collects the content subscription fee in advance and records it as deferred revenue. Refunds are offered for the remaining undelivered services, which is accounted for as variable consideration similar to the online K-12 tutoring service business. Revenue is recognized ratably over the contract period as the Group concluded that the subscription services represent a stand ready obligation to provide the services while the member simultaneously receives and consumes the benefits of such services throughout the contract period. Contract and refund liabilities The following table provides information about the Group's contract and refund liabilities arising from contract with customers. The increase in contract liabilities primarily resulted from the Group's business growth. As of December 31, 2019 2020 RMB RMB Deferred revenue-current 243,521 596,307 Deferred revenue-non current 652 1,982 Refund liabilities 5,907 22,869 Deferred revenue primarily consists of tuition fees received from customers for which the Group's revenue recognition criteria have not been met. The deferred revenue will be recognized as revenue once related service are delivered. For the years ended December 31, 2019 and 2020, revenue recognized that was included in the deferred revenue balance at January 1, 2019 and January 1, 2020 amounted to RMB75,737 and RMB243,521, respectively. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - continued Revenue recognition - continued Contract and refund liabilities - continued Refund liabilities represent the tutoring fee collected by the Group which it expects to refund back to its customer as a result of its refund policy. Refund liabilities are estimated based on the historical refund ratio for each type of courses provided. The Group's remaining performance obligations represents the amount of the transaction price for which service has not been performed. As of December 31, 2020, the aggregate amount of the transaction price allocated for the remaining performance obligations amounted to RMB598,289. The Group expects to recognize revenue of RMB596,307 and RMB1,342 related the remaining performance obligations over the next 12 months and 24 months, with the remainder of RMB640 recognized thereafter. The Group elected to apply the practical expedient to expense incremental costs of obtaining a contract when incurred as the amortization period of the contract cost that the Group otherwise would have amortized is generally less than one year. Disaggregation of revenue For the years ended December 31, 2018, 2019 and 2020, all of the Group's revenues were generated in the PRC. Additionally, all the revenues for the period were recognized from contracts with customers. The following table provides information about disaggregated revenue by types: Year ended December 31, 2018 2019 2020 RMB RMB RMB Online K-12 tutoring services 93,883 359,568 1,218,564 Other educational services 216,823 46,677 75,807 Total net revenues 310,706 406,245 1,294,371
Cost of Revenue	Cost of Revenue Cost of revenues mainly consists of salaries, welfare and service fees for instructors and tutors, rental expenses for office space, depreciation and amortization of property and equipment, teaching materials and bandwidth costs. The compensations for instructors consist of base salary, as well as teaching fees based on hourly rates and the numbers of students enrolled in connection with courses delivered. The compensation of tutors consists of base salary and performance-based compensation, which is determined based on student retention and exercise completion. The Group accrues on a monthly basis for the cost of tutors which includes base salary, compensation for exercise marking as well as student retention bonus. The retention bonus is estimated by using the expected number of successful recurring course purchase, multiplied by the bonus rate.
Research and Development Expenses	Research and development expenses Research and development expenses primarily consist of (i) salaries and benefits for development of course content, product and technology development personnel, and (ii) office rental, general expenses and depreciation expenses associated with the research and development activities. The Group's research and development activities primarily consist of the development and enhancement of the Group's educational content, applications and platforms. The Group has expensed all research and development expenses when incurred.
Sales and Marketing Expenses	Sales and marketing expenses Sales and marketing expenses primarily consist of (i) teaching materials and gifts provided for promotional online courses, (ii) salaries, benefits and commission for sales and marketing personnel, (iii) office rental, general expenses and depreciation and amortization expenses associated with the sales and marketing activities. The Group expenses advertising costs as incurred. Total advertising costs incurred were RMB5,788, RMB2,644 and RMB163,768 for the years ended December 31, 2018, 2019 and 2020, respectively.
Value Added Taxes ("VAT")	The Group's services are subject to VAT at the rate of 3% for small-scale-VAT-payer entities or at the rate of 6% for general-VAT-payer entities in accordance with relevant PRC tax rules.
Leases	Leases The Group leases offices in different cities in the PRC under operating leases. The Group determines whether an arrangement constitutes a lease at inception and records lease liabilities and right-of-use assets on its consolidated balance sheets at the lease commencement. The Group measures its lease liabilities based on the present value of the total lease payments not yet paid discounted based on its incremental borrowing rate, as the rates implicit in its leases are not determinable. The Group’s incremental borrowing rate is the estimated rate the Group would be required to pay for a collateralized borrowing equal to the total lease payments over the term of the lease. The Group estimates its incremental borrowing rate based on an analysis of publicly traded debt securities of companies with credit and financial profiles similar to its own. The Group measures right-of-use assets based on the corresponding lease liability adjusted for payments made to the lessor at or before the commencement date, and initial direct costs it incurs under the lease. The Group begins recognizing rent expense when the lessor makes the underlying asset available to the Group. The Group's leases have remaining lease terms of up to five years, some of which include options to extend the leases for an additional period which has to be agreed with the lessors based on mutual negotiation. After considering the factors that create an economic incentive, the Group did not include renewal option periods in the lease term for which it is not reasonably certain to exercise. For short-term leases, the Group records operating lease expense in its consolidated statements of operations on a straight-line basis over the lease term.
Income Taxes	Income taxes Current income taxes are provided for in accordance with the laws of the relevant tax authorities. Deferred income taxes are recognized when temporary differences exist between the tax bases of assets and liabilities and their reported amounts in the financial statements. Net operating loss carry forwards and credits are applied using enacted statutory tax rates applicable to future years. Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more-likely-than-not that a portion of or all of the deferred tax assets will not be realized. The impact of an uncertain income tax position is recognized at the largest amount that is more-likely-than-not to be sustained upon audit by the relevant tax authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Interest and penalties on income taxes are classified as a component of the provisions for income taxes.
Share-based Compensation	Share-based compensation The Company grants share options and restricted shares ("RSs") to its employees and external consultants (together, "Share-Based Awards"). The Group measures the cost of the Share-Based Awards based on the grant date fair value of the awards and recognizes compensation cost over the vesting period, which is generally the requisite service period as required by the award agreement. When no future services are required to be performed by the employee in exchange for an award of equity instruments, the cost of the award is expensed on the grant date. The Group elects to recognize forfeitures when they occur. The cancellation of an award accompanied by the concurrent grant of a replacement award is accounted for as a modification of the terms of the awards. The incremental compensation cost is measured as the excess of the fair value of the modified award over the fair value of the modified award at the modification date. The incremental portion of share-based compensation for the vested portion is recognized immediately and the incremental portion of share-based compensation for the nonvested portion is recognized over the remaining vesting period of the award. If an award is canceled without the concurrent grant of a replacement award or any other consideration, unrecognized compensation cost related to the canceled award is recognized immediately upon cancelation. For awards granted with a performance condition that affects vesting, the performance condition is not considered in determining the award’s grant-date fair value; however, the performance condition is considered when estimating the quantity of awards that are expected to vest. No compensation expense is recorded for awards with a performance condition unless and until the performance condition is determined to be probable of achievement.
Comprehensive Loss	Comprehensive loss Comprehensive loss includes net loss and foreign currency translation adjustments. Comprehensive loss is reported in the consolidated statements of comprehensive loss.
Net Loss Per Share	Net loss per share Basic loss per share is computed by dividing net loss attributable to ordinary shareholders considering the accretions to redemption value of the preferred shares, by the weighted average number of ordinary shares outstanding during the year using the two-class method. Under the two-class method, any net income is allocated between ordinary shares and other participating securities based on their participating rights. Net loss is not allocated to participating securities when the participating securities do not have a contractual obligation to share losses. The Company’s preferred shares are participating securities as they participate in undistributed earnings on an as-if-converted basis. The preferred shares have no contractual obligation to fund or otherwise absorb the Group’s losses. The Company determined that the nonvested Repurchase Right Restricted Shares (as defined in Note 10) are participating securities as the holders of the nonvested Repurchase Right Restricted Shares have a nonforfeitable right to receive dividends with all ordinary shares but the nonvested Repurchase Right Restricted Shares do not have a contractual obligation to fund or otherwise absorb the Company’s losses. Accordingly, any undistributed net income is allocated on a pro rata basis to the ordinary shares, preferred shares and nonvested Repurchase Right Restricted Shares; whereas any undistributed net loss is allocated to ordinary shares only. Diluted earnings/(loss) per share is calculated by dividing net income/(loss) attributable to ordinary shareholders, as adjusted for the accretion and allocation of net income related to the preferred shares, if any, by the weighted average number of ordinary and dilutive ordinary equivalent shares outstanding during the period. Ordinary equivalent shares consist of shares issuable upon the conversion of the preferred shares using the if-converted method, and ordinary shares issuable upon the vesting of nonvested restricted shares or exercise of outstanding share option and warrants (using the treasury stock method). Ordinary equivalent shares are calculated based on the most advantageous conversion rate or exercise price from the standpoint of the security holder. Ordinary equivalent shares are not included in the denominator of the diluted earnings per share calculation when inclusion of such shares would be anti-dilutive.
Significant Risks and Uncertainties	Significant risks and uncertainties Foreign currency risk The RMB is not a freely convertible currency. The State Administration for Foreign Exchange, under the authority of the Peoples Bank of China, controls the conversion of RMB into other currencies. The value of the RMB is subject to changes in central government policies, international economic and political developments affecting supply and demand in the China Foreign Exchange Trading System market. The Group's cash and cash equivalents denominated in RMB amounted to RMB373,915 and RMB697,097 as of December 31, 2019 and 2020, respectively. Concentration of credit risk Financial instruments that potentially expose the Group to significant concentration of credit risk primarily consist of cash and cash equivalents, restricted cash and receivables from third party payment platforms. As of December 31, 2019 and 2020, substantially all of the Group's cash and cash equivalents and restricted cash were deposited in financial institutions with high credit rating. There are no revenues from customers which individually represent greater than 10% of the total net revenues for the years ended December 31, 2018, 2019 and 2020.
Newly Adopted Accounting Pronouncements	Newly adopted accounting pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326), Measurement of Credit Losses on Financial Statements. This ASU requires a financial asset (or group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset(s) to present the net carrying value at the amount expected to be collected on the financial asset. This ASU affects entities holding financial assets and net investment in leases that are not accounted for at fair value through net income. The amendments affect loans, debt securities, trade receivables, net investments in leases, off balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope that have the contractual rights to receive cash. For public business entities, the amendments in this update are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. All entities may adopt the amendments in this update through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective (that is, a modified-retrospective approach). In April 25, 2019, ASU 2016-13 was updated with ASU 2019-04, which clarifies certain aspects of accounting for credit losses, hedging activities, and financial instruments. ASU 2019-04 provides certain alternatives for the measurement of the allowance for credit losses (ACL) on accrued interest receivable (AIR). These measurement alternatives include (1) measuring an ACL on AIR separately, (2) electing to provide separate disclosure of the AIR component of amortized cost as a practical expedient, and (3) making accounting policy elections to simplify certain aspects of the presentation and measurement of such AIR. For entities that have adopted ASU 2016-13, the amendments in ASU 2019-04 related to ASU 2016-13 are effective for fiscal years beginning after December 15, 2019, and interim periods therein. An entity may early adopt ASU 2019-04 in any interim period after its issuance if the entity has adopted ASU 2016-13. The Company adopted this ASU on January 1, 2020, and it did not have material impact to the Group’s consolidated financial statements.

Organization and Principal Ac_2

Organization and Principal Activities (Tables)	12 Months Ended
Organization and Principal Activities (Tables)	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Information About Company's Major Subsidiary and VIE	As of December 31, 2020, the Company's major subsidiary and VIE were as follows: Name ( 1) Later of date of establishment or acquisition Place of establishment Percentage of direct or indirect economic ownership Principal activities Subsidiary: Shanghai Yiqi Zuoye Information Technology Co., Ltd. ("Shanghai WFOE") April 23, 2013 PRC 100% Education services VIE: Shanghai Hexu Information Technology Co., Ltd ("Shanghai VIE") December 03, 2012 PRC 100% Education services (1) The English names are for identification purpose only.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Financial Information of VIEs and Subsidiaries Reported in Consolidated Financial Statements	The following financial information of the Company's VIEs and VIEs' subsidiaries after the elimination of inter-company transactions and balances as of December 31, 2019 and 2020 and for the years ended December 31, 2018, 2019 and 2020 was included in the accompanying consolidated financial statements: As of December 31, 2019 2020 RMB RMB Cash and cash equivalents 142,502 419,970 Restricted cash 24,653 170 Prepaid expenses and other current assets 43,628 175,002 Total current assets 210,783 595,142 Property and equipment, net 41,486 80,919 Right-of-use asset 53,875 110,939 Other non-current assets 9,804 30,475 Total non-current assets 105,165 222,333 Total assets 315,948 817,475 Short-term borrowings 9,000 - Accrued expenses and other current liabilities 151,413 213,481 Deferred revenue, current 224,092 571,827 Operating lease liabilities, current 28,179 46,835 Total current liabilities 412,684 832,143 Operating lease liabilities, non-current 18,325 56,427 Deferred revenue, non-current 652 1,982 Total non-current liabilities 18,977 58,409 Total liabilities 431,661 890,552 Year ended December 31, 2018 2019 2020 RMB RMB RMB Net revenues 97,009 362,282 1,229,126 Net (loss) income (45,056 ) (99,973 ) 301,096 Net cash generated from operating activities 31,728 159,753 347,773 Net cash used in investing activities (7,126 ) (38,396 ) (85,788 ) Net cash generated from (used in) financing activities — 9,000 (9,000 )
Schedule of Property and Equipment Estimated Useful Life	Property and equipment are stated at cost and are depreciated using the straight-line method over the estimated useful lives of the assets, as follows: Category Estimated useful life Electronic equipment 3 to 5 years Leasehold improvement Shorter of the lease term or estimated economic life Software 3 to 5 years Furniture and office equipment 5 years
Summary of Contract and Refund Liabilities Arising from Contract with Customers	The following table provides information about the Group's contract and refund liabilities arising from contract with customers. The increase in contract liabilities primarily resulted from the Group's business growth. As of December 31, 2019 2020 RMB RMB Deferred revenue-current 243,521 596,307 Deferred revenue-non current 652 1,982 Refund liabilities 5,907 22,869
Schedule of Disaggregated Revenue by Types	The following table provides information about disaggregated revenue by types: Year ended December 31, 2018 2019 2020 RMB RMB RMB Online K-12 tutoring services 93,883 359,568 1,218,564 Other educational services 216,823 46,677 75,807 Total net revenues 310,706 406,245 1,294,371

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
Prepaid Expenses and Other Current Assets (Tables)	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Summary of Prepaid Expense and Other Current Assets	Prepaid expenses and other current assets consisted of the following: As of December 31, 2019 2020 RMB RMB Prepaid VAT 21,430 71,418 Prepaid other service fees ( 1) 18,252 54,128 Prepaid advertising expenses - 52,114 Deposits 1,767 11,217 Receivables from third party payment platforms (2) 11,274 7,402 Prepaid rental expenses ( 3) 10,665 6,606 Others 2,923 8,563 66,311 211,448 (1) Prepaid other service fees mainly consisted of the prepayments for the purchase of promotion gifts, learning materials and the prepayments for third-party educational content subscription fee. The nature of such prepayment is generally short-term. (2) Receivables from third-party payment platforms consisted of cash that had been received from customers but held by the third-party payment platforms. The Group subsequently collected the full balances from the third-party payment platforms. (3) The prepaid rental expenses balance represented the prepaid rental expenses for short-term leases.

Property and Equipment,Net (Tab

Property and Equipment,Net (Tables)	12 Months Ended
Property and Equipment,Net (Tables)	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consisted of the following: As of December 31, 2019 2020 RMB RMB Electronic equipment 71,778 127,650 Leasehold improvement 35,171 47,988 Software 10,416 18,683 Furniture and office equipment 5,967 7,980 Total 123,332 202,301 Less: accumulated depreciation (58,163 ) (97,078 ) 65,169 105,223

Operating Leases (Tables)

Operating Leases (Tables)	12 Months Ended
Operating Leases (Tables)	Dec. 31, 2020
Leases Operating [Abstract]
Summary of Components of Lease Expense	The components of lease expense for the years ended December 31, 2018, 2019 and 2020 were as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Operating lease cost 23,357 45,339 72,020 Lease cost for leases with terms less than one year 3,183 10,451 26,684 Total lease cost 26,540 55,790 98,704
Summary of Maturity Analysis	The following is a maturity analysis as of December 31, 2019 and 2020: As of December 31, 2019 2020 RMB RMB 2020 45,937 - 2021 17,114 81,421 2022 6,708 69,726 2023 790 38,476 2024 - 14,807 2025 - 7,176 Less: imputed interest (6,115 ) (24,090 ) Total 64,434 187,516
Schedule of Lease Terms and Discount Rates	The following table provides a summary of the Group's lease terms and discount rates for the years ended December 31, 2018, 2019 and 2020: Year ended December 31, 2018 2019 2020 Weighted average remaining lease term (years) 2.14 1.88 3.04 Weighted average discount rate (percentage) 4.94 6.29 8.58
Summary of Supplemental Information Related to Group's Operating Leases	Supplemental information related to the Group's operating leases for the years ended December 31, 2018, 2019 and 2020 were as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Cash paid for operating leases 29,995 46,990 70,458

Other Non-current Assets (Table

Other Non-current Assets (Tables)	12 Months Ended
Other Non-current Assets (Tables)	Dec. 31, 2020
Other Assets Noncurrent [Abstract]
Summary of Other Non-current Assets	Other non-current assets consisted of the followings: As of December 31, 2019 2020 RMB RMB Prepayment for purchase of property and equipment 1,636 19,799 Rental deposits 12,278 13,875 Others 2,945 4,108 16,859 37,782

Short-term Borrowings (Tables)

Short-term Borrowings (Tables)	12 Months Ended
Short-term Borrowings (Tables)	Dec. 31, 2020
Short Term Borrowings [Abstract]
Summary of Short-term Borrowings	Short-term borrowings consisted of the followings: As of December 31, 2019 2020 RMB RMB Bank Borrowings 85,000 -

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Dec. 31, 2020
Accrued Liabilities And Other Liabilities [Abstract]
Schedule of Components of Accrued Expenses and Other Current Liabilities	The components of accrued expenses and other current liabilities were as follows: As of December 31, 2019 2020 RMB RMB Salary and welfare payable 124,191 215,551 Accrued expenses for paid and promotional courses (1) 91,319 141,163 Accrued operating expenses (2) 61,331 133,096 Refund liabilities (3) 5,907 22,869 Payable for acquisitions of property and equipment 4,096 13,024 Payable related to the IPO issuance cost - 9,684 Other tax payable 6,641 4,400 Notes payable to suppliers (4) 13,698 - Warrant liabilities 1,848 - 309,031 539,787 (1) Accrued expenses for paid and promotional courses represented accrued expenses for online K-12 tutoring services, mainly teaching material and human resource service fee to third-party service providers. (2) Accrued operating expenses mainly represented free gifts to users of in-school products, technical support expenses and other operating expenses. (3) Refund liabilities represented the estimated amounts of service fee received that is estimated to be refunded as described in Note 2. (4) Notes payable to suppliers represented the payables in relation to the production of learning materials

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	12 Months Ended
Fair Value Measurement (Tables)	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Warrant Liabilities at Fair Value	The Group measured warrant liabilities at fair value as of December 31, 2019. Fair Value Measurement at Reporting Date Using Description Fair value as of December 31, 2019 Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) RMB RMB RMB RMB Warrant liabilities 1,848 - - 1,848 Total 1,848 - - 1,848

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
Share-Based Compensation (Tables)	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Share Option Activity	Number of options Weighted average exercise price Weighted average remaining contract life Weighted average grant date fair value Aggregate intrinsic value US$ US$ US$ Outstanding as of January 1, 2020 69,721,006 0.90 6.62 0.53 44,616,903 Granted** 16,969,200 0.21 3.49 Forfeited (3,661,874 ) 1.40 1.02 Repurchased and cancelled (30,000 ) 0.0014* 0.10 Exercised (6,052,167 ) 0.0014* 0.18 Cancelled (replaced by restricted shares) (32,855,200 ) 0.0014* 1.55 Outstanding as of December 31, 2020 44,090,965 0.19 5.62 0.91 217,347,100 Vested and expect to vest as of December 31, 2020 44,090,965 0.19 5.62 0.91 217,347,100 Exercisable as of December 31, 2020 31,864,055 0.27 4.40 0.39 154,713,978 ** 1,315,000 options were granted with performance conditions. The Company recognized the compensation cost during the year ended December 31, 2020, for which it became probable that the performance target will be achieved. The Group reassessed the probability of achieving the performance target at the end of each reporting period and would record a cumulative catch-up adjustment for any changes to its assessment.
Summary of Key Assumptions Used to Determine Fair Value of Options	In determining the fair value of the share options, the binomial option pricing model was applied. The key assumptions used to determine the fair value of the options at the respective grant dates in 2018, 2019 and 2020 were as follows: For the years ended December 31, Grant date 2018 2019 2020 Expected volatility 48.3%~50.5% 50.1%~50.8% 50.1%~50.9% Risk-free interest rate 3.7%~3.9% 3.2%~3.3% 2.7%~3.2% Exercise multiples 2.2~2.8 2.2~2.8 2.2~2.8 Expected dividend yield 0.0% 0.0% 0.0% Life of options 10 years 10 years 10 years Fair value of underlying ordinary shares $1.31~$1.48 $1.32~$1.52 $1.52~$4.20
Summary of Restricted Shares	Number of Restricted Shares Grant date fair value per share US$ Outstanding as of January 1, 2020 - - Granted 5,130,305 4.20 Vested (5,130,305 ) 4.20 Cancelled - - Outstanding as of December 31, 2020 - -
Summary of Total Share-based Compensation Expense of Share Options and Restricted Shares Recognized	Total share-based compensation expense of share options and restricted shares recognized for the years ended December 31, 2018, 2019 and 2020 were as follows: For the years ended December 31 2018 2019 2020 RMB RMB RMB Sales and marketing expenses 4,911 8,737 35,077 Research and development expenses 12,254 22,508 68,688 General and administrative expenses 106,365 61,845 252,273 123,530 93,090 356,038
Employee Benefit Trust
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Restricted Shares	The following table summarized the Group’s activities of restricted shares held by the Shareholding Platform for the year ended December 31, 2020: Number of Restricted Shares Grant date fair value per share US$ Outstanding as of January 1, 2020 - - Granted (to replace existing options) 32,855,200 3.0 Vested (14,326,831 ) 2.7 Cancelled - - Outstanding as of December 31, 2020 18,528,369 3.2

Convertible Redeemable Prefer_2

Convertible Redeemable Preferred Shares (Tables)	12 Months Ended
Convertible Redeemable Preferred Shares (Tables)	Dec. 31, 2020
Temporary Equity Disclosure [Abstract]
Rollforward of Carrying Amount of Convertible Redeemable Preferred Shares	The following table summarized the roll forward of the carrying amount of the convertible redeemable preferred shares for the years ended December 31, 2018, 2019 and 2020: Series B Series B+ Series C Series D Series E Series F Total RMB RMB RMB RMB RMB RMB RMB January 1, 2018 322,238 503,116 488,780 928,472 - - 2,242,606 Issuance - - - - 1,588,067 - 1,588,067 Accretion (32,313 ) (50,491 ) (44,257 ) 139,272 232,160 - 244,371 December 31, 2018 289,925 452,625 444,523 1,067,744 1,820,227 - 4,075,044 Issuance - - - - - - - Accretion 40,892 63,844 60,198 160,161 275,440 - 600,535 December 31, 2019 330,817 516,469 504,721 1,227,905 2,095,667 - 4,675,579 Issuance - - - - - 849,528 849,528 Accretion 559,428 873,734 804,702 170,197 292,699 137,231 2,837,991 Conversion (890,245 ) (1,390,203 ) (1,309,423 ) (1,398,102 ) (2,388,366 ) (986,759 ) (8,363,098 ) December 31, 2020 - - - - - - - As of December 31, 2020, a summary of convertible redeemable preferred shares is as follows: Series Average Issue Price Per Share Issue Date Shares Issued Shares outstanding as of January 1, 2019 and 2020 Issuance of convertible redeemable preferred shares Conversion of the convertible redeemable preferred shares upon the IPO Shares outstanding as of December 31, 2020 Proceeds from issuance, net of issuance cost Carrying Amount as of December 31, 2020 US$ RMB RMB B 0.1738 06/06/2013 34,815,112 34,544,762 - (34,544,762 ) - 37,122 - B+ 0.1849 09/06/2013 54,083,288 54,083,288 - (54,083,288 ) - 61,202 - C 0.3586 04/12/2014 50,195,203 50,195,203 - (50,195,203 ) - 111,800 - D 1.9923 03/09/2015 50,193,243 50,193,243 - (50,193,243 ) - 626,350 - E 3.1716 01/12/2018 78,824,567 78,824,567 - (78,824,567 ) - 1,588,067 - F 3.6159 06/26/2020 33,186,759 - 33,186,759 (33,186,759 ) - 849,528 - 301,298,172 267,841,063 33,186,759 (301,027,822 ) - 3,274,069 -

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Summary of Principal Components of Deferred Taxes	12. INCOME TAXES – continued PRC - continued The principal components of deferred taxes were as follows: As of December 31, 2018 2019 2020 RMB RMB RMB Deferred tax assets Accrued expenses 7,242 9,231 12,142 Advertising expenses carrying forwards - - 24,202 Depreciation of property and equipment 1,318 853 388 Net operating loss carrying forwards 295,682 503,212 724,597 Total deferred tax assets 304,242 513,296 761,329 Less: valuation allowance (304,242 ) (513,296 ) (761,329 ) Deferred tax assets, net - - -
Summary of Reconciliation of Effective Tax Rate And Statutory Income Tax Rate	The reconciliation of the effective tax rate and the statutory income tax rate applicable to PRC operations was as follow: Year ended December 31, 2018 2019 2020 RMB RMB RMB Loss before provision for income taxes (656,071 ) (963,750 ) (1,339,908 ) Income tax benefit computed at an applicable tax rate of 25% (164,018 ) (240,938 ) (334,977 ) Effect of non-deductible expenses 2,821 3,738 11,540 Effect of research and development expenses super deduction (2,361 ) (10,740 ) (24,037 ) Effect of preferential tax rate 6,988 18,413 18,513 Effect on tax rates in different tax jurisdictions 30,113 20,473 80,928 Change in valuation allowance 126,457 209,054 248,033 - - -
Summary of Movements of Valuation Allowance	The movements of valuation allowance for the years end December 31, 2018, 2019 and 2020 are as follows: Year ended December 31, 2018 2019 2020 RMB RMB RMB Balance at beginning of the period 177,785 304,242 513,296 Additions 126,457 209,054 248,033 Reversal - - - Balance at end of the period 304,242 513,296 761,329

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
Net Loss Per Share (Tables)	Dec. 31, 2020
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of basic and diluted net loss per share for the periods Year ended December 31, 2018 2019 2020 RMB RMB RMB Numerator: Net loss attributable to ordinary shareholders (900,442 ) (1,564,285 ) (4,177,899 ) Denominator: Weighted average ordinary shares outstanding used in computing basic and diluted net loss per share 48,676,298 57,410,827 93,503,437 Basic and diluted loss per share (18.50 ) (27.25 ) (44.68 )
Summary of Shares Outstanding Excluded from Calculation of Diluted Net Loss Per Ordinary Share	For the years ended December 31, 2018, 2019 and 2020, the following shares outstanding were excluded from the calculation of diluted net loss per ordinary share, as their inclusion would have been anti-dilutive for the periods prescribed. Year ended December 31, 2018 2019 2020 Shares issuable upon exercise of share options 55,957,332 69,409,835 55,825,379 Shares issuable upon vesting of restricted shares 12,914,110 423,804 9,272,591 Shares issuable upon conversion of Series A convertible preferred shares 17,085,275 17,085,275 - Shares issuable upon conversion of Series B convertible redeemable preferred shares 34,544,762 34,544,762 - Shares issuable upon conversion of Series B+ convertible redeemable preferred shares 54,083,288 54,083,288 - Shares issuable upon conversion of Series C convertible redeemable preferred shares 50,195,203 50,195,203 - Shares issuable upon conversion of Series D convertible redeemable preferred shares 50,193,243 50,193,243 - Shares issuable upon conversion of Series E convertible redeemable preferred shares 76,449,032 78,824,567 - Warrants (Note 8) - 4,959 -

Related Party Transaction (Tabl

Related Party Transaction (Tables)	12 Months Ended
Related Party Transaction (Tables)	Dec. 31, 2020
Related Party Transactions [Abstract]
Summary of Significant Balances Between Group and Related Party	The significant balances between the Group and its related party were as follows: As of December 31, 2019 2020 RMB RMB Amounts due from: Fluency Holding Ltd. 2,611 - Total 2,611 -

Organization and Principal Ac_3

Organization and Principal Activities - Schedule of Information About Company's Major Subsidiary and VIE (Details)	12 Months Ended
	Dec. 31, 2020
Subsidiary
Organization And Principal Activities [Line Items]
Name	Shanghai Yiqi Zuoye Information TechnologyCo., Ltd. ("Shanghai WFOE")
Later of date of establishment or acquisition	Apr. 23, 2013
Place of establishment	PRC
Percentage of direct or indirect economic ownership	100.00%
Principal activities	Education services
VIEs
Organization And Principal Activities [Line Items]
Name	Shanghai Hexu Information TechnologyCo., Ltd. ("Shanghai VIE")
Later of date of establishment or acquisition	Dec. 3, 2012
Place of establishment	PRC
Percentage of direct or indirect economic ownership	100.00%
Principal activities	Education services

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)	Dec. 31, 2020USD ($)	Jan. 01, 2020CNY (¥)	Jan. 01, 2019CNY (¥)
Summary of Significant Accounting Policies [Line Items]
VIEs, consolidated assets, percentage	24.00%	34.00%		24.00%
VIEs, consolidated liabilities, percentage	67.00%	61.00%		67.00%
USD exchange rate	6.5250			6.5250
Impairment loss on long-lived assets	¥ 0	¥ 0	¥ 0
Deferred revenue, current	596,307,000	243,521,000		$ 91,388	¥ 243,521,000	¥ 75,737,000
Deferred revenue	598,289,000
Advertising costs	163,768,000	2,644,000	5,788,000
Cash and cash equivalents	2,834,962,000	653,859,000	¥ 1,252,983,000	$ 434,477
Foreign Exchange
Summary of Significant Accounting Policies [Line Items]
Cash and cash equivalents	¥ 697,097,000	373,915,000
Minimum
Summary of Significant Accounting Policies [Line Items]
Value added tax rate	3.00%
Maximum
Summary of Significant Accounting Policies [Line Items]
Value added tax rate	6.00%
Remaining lease terms	5 years			5 years
VIE
Summary of Significant Accounting Policies [Line Items]
Deferred revenue, current	¥ 571,827,000	224,092,000
Cash and cash equivalents	419,970,000	¥ 142,502,000
Exclusive Call Option Agreement \| VIE
Summary of Significant Accounting Policies [Line Items]
Purchase price of WFOE to purchase equity interests of VIEs	¥ 1
Initial term	10 years
Period for which exclusive call option agreement shall remain effective upon the written notice issued by WFOE	10 days

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Financial Information of VIEs and Subsidiaries Reported in Consolidated Financial Statements (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)	Dec. 31, 2020USD ($)	Jan. 01, 2020CNY (¥)	Jan. 01, 2019CNY (¥)
Variable Interest Entity [Line Items]
Cash and cash equivalents	¥ 2,834,962		¥ 653,859	¥ 1,252,983	$ 434,477
Restricted cash	170		34,843	22,861	26
Prepaid expenses and other current assets	211,448		66,311		32,406
Total current assets	3,046,580		757,624		466,909
Property and equipment, net	105,223		65,169		16,126
Right-of-use assets	200,157		78,637		30,675
Other non-current assets	37,782		16,859		5,790
TOTAL ASSETS	3,389,742		918,289		519,500
Short-term borrowings			85,000
Accrued expenses and other current liabilities	539,787		309,031		82,725
Deferred revenue, current	596,307		243,521		91,388	¥ 243,521	¥ 75,737
Operating lease liabilities, current	69,409		43,152		10,637
Total current liabilities	1,205,503		680,704		184,750
Operating lease liabilities, non-current	118,107		21,282		18,101
Deferred revenue, non-current	1,982		652		304
TOTAL LIABILITIES	1,325,592		702,638		$ 203,155
Net revenues	1,294,371	$ 198,371	406,245	310,706
Net (loss) income	(1,339,908)	(205,349)	(963,750)	(656,071)
Net cash generated from operating activities	(522,988)	(80,150)	(631,288)	(418,865)
Net cash used in investing activities	(89,504)	(13,717)	(28,594)	(48,947)
Net cash generated from (used in) financing activities	2,797,421	$ 428,724	84,449	1,550,372
VIEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	419,970		142,502
Restricted cash	170		24,653
Prepaid expenses and other current assets	175,002		43,628
Total current assets	595,142		210,783
Property and equipment, net	80,919		41,486
Right-of-use assets	110,939		53,875
Other non-current assets	30,475		9,804
Total non-current assets	222,333		105,165
TOTAL ASSETS	817,475		315,948
Short-term borrowings			9,000
Accrued expenses and other current liabilities	213,481		151,413
Deferred revenue, current	571,827		224,092
Operating lease liabilities, current	46,835		28,179
Total current liabilities	832,143		412,684
Operating lease liabilities, non-current	56,427		18,325
Deferred revenue, non-current	1,982		652
Total non-current liabilities	58,409		18,977
TOTAL LIABILITIES	890,552		431,661
Net revenues	1,229,126		362,282	97,009
Net (loss) income	301,096		(99,973)	(45,056)
Net cash generated from operating activities	347,773		159,753	31,728
Net cash used in investing activities	(85,788)		(38,396)	¥ (7,126)
Net cash generated from (used in) financing activities	¥ (9,000)		¥ 9,000

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Life (Details)	12 Months Ended
	Dec. 31, 2020
Electronic Equipment \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	3 years
Electronic Equipment \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Leasehold Improvement
Property Plant And Equipment [Line Items]
Estimated useful life	Shorter of the lease term or estimated economic life
Software \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	3 years
Software \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Estimated useful life	5 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Contract and Refund Liabilities Arising from Contract with Customers (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Jan. 01, 2020CNY (¥)	Dec. 31, 2019CNY (¥)	Jan. 01, 2019CNY (¥)
Contract With Customer Refund Liability [Abstract]
Deferred revenue, current	¥ 596,307	$ 91,388	¥ 243,521	¥ 243,521	¥ 75,737
Deferred revenue, non-current	1,982	$ 304		652
Refund liabilities	¥ 22,869			¥ 5,907

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Additional Information (Details 1) ¥ in Thousands	Dec. 31, 2020CNY (¥)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Summary of Significant Accounting Policies [Line Items]
Revenue, remaining performance obligation, amount	¥ 596,307
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Summary of Significant Accounting Policies [Line Items]
Revenue, remaining performance obligation, amount	¥ 1,342
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Summary of Significant Accounting Policies [Line Items]
Revenue, remaining performance obligation, amount	¥ 640
Revenue, remaining performance obligation, expected timing of satisfaction, period	0 years

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Schedule of Disaggregated Revenue by Types (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Disaggregation Of Revenue [Line Items]
Revenues	¥ 1,294,371	$ 198,371	¥ 406,245	¥ 310,706
Online K-12 Tutoring Services
Disaggregation Of Revenue [Line Items]
Revenues	1,218,564		359,568	93,883
Other Educational Services
Disaggregation Of Revenue [Line Items]
Revenues	¥ 75,807		¥ 46,677	¥ 216,823

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)
Prepaid Expense And Other Assets Current [Abstract]
Prepaid VAT	¥ 71,418		¥ 21,430
Prepaid other service fees	54,128		18,252
Prepaid advertising expenses	52,114
Deposits	11,217		1,767
Receivables from third party payment platforms	7,402		11,274
Prepaid rental expenses	6,606		10,665
Others	8,563		2,923
Prepaid expenses and other current assets	¥ 211,448	$ 32,406	¥ 66,311

Property and Equipment,Net - Su

Property and Equipment,Net - Summary of Property and Equipment (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)
Property Plant And Equipment [Line Items]
Property, equipment and software, gross	¥ 202,301		¥ 123,332
Less: accumulated depreciation	(97,078)		(58,163)
Property, equipment and software, net	105,223	$ 16,126	65,169
Electronic Equipment
Property Plant And Equipment [Line Items]
Property, equipment and software, gross	127,650		71,778
Leasehold Improvement
Property Plant And Equipment [Line Items]
Property, equipment and software, gross	47,988		35,171
Software
Property Plant And Equipment [Line Items]
Property, equipment and software, gross	18,683		10,416
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property, equipment and software, gross	¥ 7,980		¥ 5,967

Property and Equipment,Net - Ad

Property and Equipment,Net - Additional Information (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Property Plant And Equipment [Abstract]
Depreciation expenses	¥ 39,700	$ 6,084	¥ 22,675	¥ 15,760

Operating Leases - Summary of C

Operating Leases - Summary of Components of Lease Expense (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease Cost [Abstract]
Operating lease cost	¥ 72,020	¥ 45,339	¥ 23,357
Lease cost for leases with terms less than one year	26,684	10,451	3,183
Total lease cost	¥ 98,704	¥ 55,790	¥ 26,540

Operating Leases - Summary of M

Operating Leases - Summary of Maturity Analysis (Details) - CNY (¥) ¥ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Lease Liabilities Payments Due [Abstract]
2020		¥ 45,937
2021	¥ 81,421	17,114
2022	69,726	6,708
2023	38,476	790
2024	14,807
2025	7,176
Less: imputed interest	(24,090)	(6,115)
Total	¥ 187,516	¥ 64,434

Operating Leases - Summary of G

Operating Leases - Summary of Group's Lease Terms and Discount Rates (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease Cost [Abstract]
Weighted average remaining lease term (years)	3 years 14 days	1 year 10 months 17 days	2 years 1 month 20 days
Weighted average discount rate (percentage)	8.58%	6.29%	4.94%

Operating Leases - Summary of S

Operating Leases - Summary of Supplemental Information Related to Group's Operating Leases (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease Cost [Abstract]
Cash paid for operating leases	¥ 70,458	¥ 46,990	¥ 29,995

Other Non-current Assets - Summ

Other Non-current Assets - Summary of Other Non-current Assets (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)
Other Assets Noncurrent [Abstract]
Prepayment for purchase of property and equipment	¥ 19,799		¥ 1,636
Rental deposits	13,875		12,278
Others	4,108		2,945
Other non-current assets	¥ 37,782	$ 5,790	¥ 16,859

Short-term Borrowings - Summary

Short-term Borrowings - Summary of Short-term Borrowings (Details) ¥ in Thousands	Dec. 31, 2019CNY (¥)
Short Term Debt [Line Items]
Short-term borrowings	¥ 85,000
Bank Borrowings
Short Term Debt [Line Items]
Short-term borrowings	¥ 85,000

Short-term Borrowings - Additio

Short-term Borrowings - Additional Information (Details) - CNY (¥) ¥ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2019
Short Term Debt [Line Items]
Proceeds from short-term borrowings		¥ 85,000
PRC Commercial Bank
Short Term Debt [Line Items]
Proceeds from short-term borrowings		¥ 67,000
Fixed interest rate		2.35%
PRC Commercial Bank \| VIE and Subsidiary
Short Term Debt [Line Items]
Proceeds from short-term borrowings	¥ 9,000
Fixed interest rate	4.35%
Loans pledged as restricted term deposits	¥ 20,000

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Components of Accrued Expenses and Other Current Liabilities (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)
Accrued Liabilities And Other Liabilities [Abstract]
Salary and welfare payable	¥ 215,551		¥ 124,191
Accrued expenses for paid and promotional courses	141,163		91,319
Accrued operating expenses	133,096		61,331
Refund liabilities	22,869		5,907
Payable for acquisitions of property and equipment	13,024		4,096
Payable related to the IPO issuance cost	9,684
Other tax payable	4,400		6,641
Notes payable to suppliers			13,698
Warrant liabilities			1,848
Accrued expenses and other current liabilities	¥ 539,787	$ 82,725	¥ 309,031

Fair Value Measurement - Summar

Fair Value Measurement - Summary of Warrant Liabilities at Fair Value (Details) - Fair Value Measurements, Recurring ¥ in Thousands	Dec. 31, 2019CNY (¥)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value	¥ 1,848
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value	1,848
Warrant Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value	1,848
Warrant Liabilities \| Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities fair value	¥ 1,848

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details)

Nov. 12, 2020shares

Jan. 16, 2019CNY (¥)shares

Jan. 12, 2018Installment$ / sharesshares

Mar. 09, 2015shares

Dec. 31, 2020CNY (¥)shares

Nov. 30, 2020CNY (¥)shares

Oct. 31, 2020$ / sharesshares

Sep. 30, 2020CNY (¥)shares

Sep. 30, 2020USD ($)$ / sharesshares

Jun. 30, 2020$ / sharesshares

Mar. 31, 2020CNY (¥)

Dec. 31, 2020CNY (¥)Installmentshares

Dec. 31, 2020USD ($)Installment$ / sharesshares

Dec. 31, 2019CNY (¥)

Dec. 31, 2018CNY (¥)

Dec. 31, 2020$ / shares

Mar. 31, 2020$ / shares

Dec. 31, 2019$ / shares

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Weighted average exercise price | $ / shares

$ 0.19

$ 0.90

Compensation expense | ¥

¥ 48,683,000

¥ 133,975,000

¥ 46,122,000

¥ 29,406,000

Unrecognized compensation expense | ¥

¥ 208,844,000

¥ 137,670,000

Weighted-average period for unrecognized compensation expense to be recognized

3 years 10 months 9 days

3 years 7 months 2 days

Payment for Repurchase of Vested Options | ¥

¥ 528,000

¥ 1,355,000

23,948,000

Weighted average exercise price, Granted | $ / shares

$ 0.21

Common stock, par value | $ / shares

0.0001

$ 0.0001

Restricted Share Purchase Agreement with Founder

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Compensation expense | ¥

¥ 140,706,000

¥ 46,968,000

¥ 94,124,000

Modification of Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of options | shares

46,568,242

2015 Share Option Plan | Maximum

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares, granted | shares

59,899,375

Options vesting period

5 years

2015 Share Option Plan | Minimum

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Options vesting period

2 years

2018 Share Option Plan | Maximum

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares, granted | shares

25,703,602

2020 Share Incentive Plan

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares granted | shares

5,130,305

2020 Share Incentive Plan | Maximum

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares, granted | shares

20,521,221

Annual increase, percentage of issued and outstanding shares

2.00%

2020 Share Incentive Plan | Maximum | Modification of Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Stock option exercise price | $ / shares

$ 0.0014

Incremental costs | ¥

¥ 239,044,000

Incremental costs for options exercisable after completion of IPO | ¥

84,648,000

Incremental costs | ¥

154,396,000

Compensation expense | ¥

¥ 39,766,000

Restricted Share Purchase Agreement With Shareholding Platform | Employee Benefit Trust

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares granted | shares

32,855,200

Compensation expense | ¥

¥ 44,625,000

Weighted-average period for unrecognized compensation expense to be recognized

3 years 4 months 17 days

Weighted average exercise price, Granted | $ / shares

$ 0.0014

Unrecognized compensation costs | ¥

¥ 331,840,000

Restricted Share Purchase Agreement with Founder

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Compensation expense | ¥

¥ 36,732,000

Stock repurchase program number of shares authorized to be repurchased | shares

4,135,320

Total consideration

¥ 105,644,000

$ 14,953,000

Consideration per share | $ / shares

$ 3.6159

Restricted Share Purchase Agreement with Founder | Series D Preferred Shares

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares granted | shares

7,528,956

Weighted-average period for unrecognized compensation expense to be recognized

4 years

Ordinary shares issued | shares

25,449,238

Common stock, par value | $ / shares

$ 0.0001

Ordinary shares issued to replace previously granted nonvested options which were cancelled | shares

17,920,282

Number of equal monthly installments starting from grant date | Installment

Repurchase right, minimum equity valuation prior to trade | $

$ 1,200,000,000

Repurchase right, minimum equity valuation prior to equity financing | $

$ 1,200,000,000

Service period of compensation expense recognized

4 years

Restricted Share Purchase Agreement with Founder | Series E Convertible Redeemable Preferred Shares

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares granted | shares

12,851,801

Unrecognized compensation costs | ¥

¥ 42,910,000

Common stock, par value | $ / shares

$ 0.0001

Number of equal installments | Installment

Number of shares founder waived his right to receive the third installment | shares

4,283,934

Restricted Share Purchase Agreement with Founder | Restricted Stock Units (RSUs)

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares granted | shares

5,130,305

Sale of stock, consideration received on transaction | ¥

¥ 0

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options, Beginning balance	69,721,006
Number of options, Granted	16,969,200
Number of options, Forfeited	(3,661,874)
Number of options, Repurchased and cancelled	(30,000)
Number of options, Exercised	(6,052,167)
Number of options, Cancelled (replaced by restricted shares)	(32,855,200)
Number of options, Ending balance	44,090,965	69,721,006
Number of options, Vested and expect to vest, Ending balance	44,090,965
Number of options, Exercisable, Ending balance	31,864,055
Weighted average exercise price, Beginning balance	$ 0.90
Weighted average exercise price, Granted	0.21
Weighted average exercise price, Forfeited	1.40
Weighted average exercise price, Repurchased and cancelled	0.0014
Weighted average exercise price, Exercised	0.0014
Weighted average exercise price, Cancelled (replaced by restricted shares)	0.0014
Weighted average exercise price, Ending Balance	0.19	$ 0.90
Weighted average exercise price, Vested and expect to vest, Ending balance	0.19
Weighted average exercise price, Exercisable, Ending balance	$ 0.27
Weighted average remaining contract life, Beginning balance	5 years 7 months 13 days	6 years 7 months 13 days
Weighted average exercise price, Vested and expect to vest, Ending balance	5 years 7 months 13 days
Weighted average remaining contract life, Exercisable, Ending balance	4 years 4 months 24 days
Weighted average grant date fair value, Beginning balance	$ 0.53
Weighted average grant date fair value, Granted	3.49
Weighted average grant date fair value, Forfeited	1.02
Weighted average grant date fair value, Repurchased and cancelled	0.10
Weighted average grant date fair value, Exercised	0.18
Weighted average grant date fair value, Cancelled (replaced by restricted shares)	1.55
Weighted average grant date fair value, Ending balance	0.91	$ 0.53
Weighted average grant date fair value, Vested and expect to vest, Ending balance	0.91
Weighted average grant date fair value, Exercisable, Ending balance	$ 0.39
Aggregate intrinsic value, Ending balance	$ 217,347,100	$ 44,616,903
Aggregate intrinsic value, Vested and expect to vest, Ending balance	217,347,100
Aggregate intrinsic value, Exercisable, Ending balance	$ 154,713,978

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Share Option Activity (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options, Granted	16,969,200
2020 Share Incentive Plan \| Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options, Granted	1,315,000

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Key Assumptions Used to Determine Fair Value of Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of underlying ordinary shares	$ 3.49
2020 Share Incentive Plan \| Share Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	50.10%	50.10%	48.30%
Expected volatility, maximum	50.90%	50.80%	50.50%
Risk-free interest rate, minimum	2.70%	3.20%	3.70%
Risk-free interest rate, maximum	3.20%	3.30%	3.90%
Expected dividend yield	0.00%	0.00%	0.00%
Life of options	10 years	10 years	10 years
2020 Share Incentive Plan \| Share Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise multiples	$ 2.2	$ 2.2	$ 2.2
Fair value of underlying ordinary shares	1.52	1.32	1.31
2020 Share Incentive Plan \| Share Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise multiples	2.8	2.8	2.8
Fair value of underlying ordinary shares	$ 4.20	$ 1.52	$ 1.48

Share-Based Compensation - Su_4

Share-Based Compensation - Summary of Restricted Shares (Details)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Restricted Share Purchase Agreement With Shareholding Platform
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value per share, Granted (to replace existing options) \| $ / shares	$ 3
Grant date fair value per share, Vested \| $ / shares	2.7
Grant date fair value per share, Ending balance \| $ / shares	$ 3.2
Restricted Share Purchase Agreement With Shareholding Platform \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of restricted shares, Granted (to replace existing options)	32,855,200
Number of restricted shares, Vested	(14,326,831)
Number of restricted shares, Ending balance	18,528,369
Number of shares granted	32,855,200
Restricted Share Purchase Agreement with Founder
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value per share, Granted (to replace existing options) \| $ / shares	$ 4.20
Grant date fair value per share, Vested \| $ / shares	$ 4.20
Restricted Share Purchase Agreement with Founder \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of restricted shares, Granted (to replace existing options)	5,130,305
Number of restricted shares, Vested	(5,130,305)
Number of shares granted	5,130,305

Share-Based Compensation - Su_5

Share-Based Compensation - Summary of Total Share-Based Compensation Expense of Share Options and Restricted Shares Recognized (Details) - CNY (¥) ¥ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation expense	¥ 48,683	¥ 133,975	¥ 46,122	¥ 29,406
Share Options and Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation expense		356,038	93,090	123,530
Share Options and Restricted Shares \| Sales and Marketing Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation expense		35,077	8,737	4,911
Share Options and Restricted Shares \| Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation expense		68,688	22,508	12,254
Share Options and Restricted Shares \| General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation expense		¥ 252,273	¥ 61,845	¥ 106,365

Convertible Redeemable Prefer_3

Convertible Redeemable Preferred Shares - Additional Information (Details) $ / shares in Units, ¥ in Thousands	1 Months Ended				12 Months Ended
	Jun. 30, 2020CNY (¥)	Jun. 30, 2020USD ($)$ / sharesshares	Jan. 31, 2018CNY (¥)	Jan. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2018CNY (¥)	Dec. 31, 2019shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued						301,298,172
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares \| ¥					¥ 3,274,069		¥ 1,588,067
Convertible preferred stock, terms of conversion					Each holder of convertible redeemable preferred shares shall have the right, at such holder's sole discretion, to convert all or any portion of the preferred shares into ordinary shares on a one-for-one basis at any time. The initial conversion price is the issuance price of preferred shares, subject to adjustment in the event of (1) share dividends, subdivisions, combinations or consolidation of ordinary shares, (2) reclassification, exchange and substitution, and (3) issuance of new securities at a price per share less than the applicable conversion price in effect on the date of and immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance.	Each holder of convertible redeemable preferred shares shall have the right, at such holder's sole discretion, to convert all or any portion of the preferred shares into ordinary shares on a one-for-one basis at any time. The initial conversion price is the issuance price of preferred shares, subject to adjustment in the event of (1) share dividends, subdivisions, combinations or consolidation of ordinary shares, (2) reclassification, exchange and substitution, and (3) issuance of new securities at a price per share less than the applicable conversion price in effect on the date of and immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance.
Convertible redeemable preferred shares conversion basis ratio					100.00%	100.00%
Proceeds from issuance initial public offering					¥ 2,051,695	$ 314,436,000
Temporary equity redemption period					48th month	48th month
Preferred shares percentage of liquidation preference					100.00%	100.00%
IPO
Temporary Equity [Line Items]
Proceeds from issuance initial public offering \| ¥					¥ 2,023,593
IPO \| Minimum
Temporary Equity [Line Items]
Equity valuation of the company \| $						$ 2,000,000,000
Proceeds from issuance initial public offering \| $						$ 100,000,000
Series B Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued						34,815,112		34,544,762
Convertible redeemable preferred shares, issue price \| $ / shares						$ 0.1738
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares \| ¥					¥ 37,122
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%
Series B+ Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued						54,083,288
Convertible redeemable preferred shares, issue price \| $ / shares						$ 0.1849
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares \| ¥					¥ 61,202
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%
Series C Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued						50,195,203		50,195,203
Convertible redeemable preferred shares, issue price \| $ / shares						$ 0.3586
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares \| ¥					¥ 111,800
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%
Series D Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued						50,193,243		50,193,243
Convertible redeemable preferred shares, issue price \| $ / shares						$ 1.9923
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares \| ¥					¥ 626,350
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%
Series E Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued				78,824,567		78,824,567		78,824,567
Convertible redeemable preferred shares, issue price \| $ / shares				$ 3.1716		$ 3.1716
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares			¥ 1,603,837	$ 250,000,000	¥ 1,588,067
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%
Convertible redeemable preferred shares, held by Founder						3,305,651
Series F Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Convertible redeemable preferred shares, shares issued		33,186,759				33,186,759
Convertible redeemable preferred shares, issue price \| $ / shares		$ 3.6159				$ 3.6159
Total cash proceeds/consideration from issuance of convertible redeemable preferred shares	¥ 849,528	$ 120,000,000			¥ 849,528	$ 130,196,000
Redemption price percentage of applicable issue price					100.00%	100.00%
Percentage compound per annum return from issue date					15.00%	15.00%

Convertible Redeemable Prefer_4

Convertible Redeemable Preferred Shares - Rollforward of Carrying Amount of Convertible Redeemable Preferred Shares (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Temporary Equity [Line Items]
Beginning Balance	¥ 4,675,579		¥ 4,075,044	¥ 2,242,606
Issuance	849,528			1,588,067
Accretion	2,837,991	$ 434,941	600,535	244,371
Conversion	(8,363,098)
Ending Balance			4,675,579	4,075,044
Series B Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Beginning Balance	330,817		289,925	322,238
Accretion	559,428		40,892	(32,313)
Conversion	(890,245)
Ending Balance			330,817	289,925
Series B+ Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Beginning Balance	516,469		452,625	503,116
Accretion	873,734		63,844	(50,491)
Conversion	(1,390,203)
Ending Balance			516,469	452,625
Series C Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Beginning Balance	504,721		444,523	488,780
Accretion	804,702		60,198	(44,257)
Conversion	(1,309,423)
Ending Balance			504,721	444,523
Series D Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Beginning Balance	1,227,905		1,067,744	928,472
Accretion	170,197		160,161	139,272
Conversion	(1,398,102)
Ending Balance			1,227,905	1,067,744
Series E Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Beginning Balance	2,095,667		1,820,227
Issuance				1,588,067
Accretion	292,699		275,440	232,160
Conversion	(2,388,366)
Ending Balance			¥ 2,095,667	¥ 1,820,227
Series F Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Issuance	849,528
Accretion	137,231
Conversion	¥ (986,759)

Convertible Redeemable Prefer_5

Convertible Redeemable Preferred Shares - Summary of Convertible Redeemable Preferred Shares (Details) $ / shares in Units, ¥ in Thousands, $ in Thousands	1 Months Ended				12 Months Ended
	Jun. 30, 2020CNY (¥)	Jun. 30, 2020USD ($)$ / sharesshares	Jan. 31, 2018CNY (¥)	Jan. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2020CNY (¥)shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2018CNY (¥)	Dec. 31, 2019shares
Temporary Equity [Line Items]
Shares Issued						301,298,172
Shares outstanding as of January 1, 2019 and 2020					267,841,063	267,841,063
Issuance of convertible redeemable preferred shares					33,186,759	33,186,759
Conversion of the convertible redeemable preferred shares upon the IPO					(301,027,822)	(301,027,822)
Net proceeds from the issuance of convertible redeemable preferred shares \| ¥					¥ 3,274,069		¥ 1,588,067
Series B Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares						$ 0.1738
Issue Date					Jun. 6, 2013	Jun. 6, 2013
Shares Issued						34,815,112		34,544,762
Shares outstanding as of January 1, 2019 and 2020					34,544,762	34,544,762
Conversion of the convertible redeemable preferred shares upon the IPO					(34,544,762)	(34,544,762)
Net proceeds from the issuance of convertible redeemable preferred shares \| ¥					¥ 37,122
Series B+ Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares						$ 0.1849
Issue Date					Sep. 6, 2013	Sep. 6, 2013
Shares Issued						54,083,288
Shares outstanding as of January 1, 2019 and 2020					54,083,288	54,083,288
Conversion of the convertible redeemable preferred shares upon the IPO					(54,083,288)	(54,083,288)
Net proceeds from the issuance of convertible redeemable preferred shares \| ¥					¥ 61,202
Series C Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares						$ 0.3586
Issue Date					Apr. 12, 2014	Apr. 12, 2014
Shares Issued						50,195,203		50,195,203
Shares outstanding as of January 1, 2019 and 2020					50,195,203	50,195,203
Conversion of the convertible redeemable preferred shares upon the IPO					(50,195,203)	(50,195,203)
Net proceeds from the issuance of convertible redeemable preferred shares \| ¥					¥ 111,800
Series D Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares						$ 1.9923
Issue Date					Mar. 9, 2015	Mar. 9, 2015
Shares Issued						50,193,243		50,193,243
Shares outstanding as of January 1, 2019 and 2020					50,193,243	50,193,243
Conversion of the convertible redeemable preferred shares upon the IPO					(50,193,243)	(50,193,243)
Net proceeds from the issuance of convertible redeemable preferred shares \| ¥					¥ 626,350
Series E Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares				$ 3.1716		$ 3.1716
Issue Date					Jan. 12, 2018	Jan. 12, 2018
Shares Issued				78,824,567		78,824,567		78,824,567
Shares outstanding as of January 1, 2019 and 2020					78,824,567	78,824,567
Conversion of the convertible redeemable preferred shares upon the IPO					(78,824,567)	(78,824,567)
Net proceeds from the issuance of convertible redeemable preferred shares			¥ 1,603,837	$ 250,000	¥ 1,588,067
Series F Convertible Redeemable Preferred Shares
Temporary Equity [Line Items]
Average Issue Price Per Share \| $ / shares		$ 3.6159				$ 3.6159
Issue Date					Jun. 26, 2020	Jun. 26, 2020
Shares Issued		33,186,759				33,186,759
Issuance of convertible redeemable preferred shares					33,186,759	33,186,759
Conversion of the convertible redeemable preferred shares upon the IPO					(33,186,759)	(33,186,759)
Net proceeds from the issuance of convertible redeemable preferred shares	¥ 849,528	$ 120,000			¥ 849,528	$ 130,196

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	Apr. 01, 2018HKD ($)	Jan. 01, 2008	Dec. 31, 2020CNY (¥)	Dec. 31, 2020KYD ($)	Dec. 31, 2020HKD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2019KYD ($)	Dec. 31, 2019HKD ($)	Dec. 31, 2018CNY (¥)	Dec. 31, 2018KYD ($)	Dec. 31, 2018HKD ($)
Income Tax Examination [Line Items]
Income tax expenses \| ¥
Significant unrecognized uncertain tax positions \| ¥			¥ 0			¥ 0			¥ 0
PRC Entities
Income Tax Examination [Line Items]
Effective income tax rate			25.00%	25.00%	25.00%
Operating loss carryforwards \| ¥			¥ 3,056,123,000
PRC Entities \| Minimum
Income Tax Examination [Line Items]
Operating loss carryforwards, expiration date			Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2021
PRC Entities \| Maximum
Income Tax Examination [Line Items]
Operating loss carryforwards, expiration date			Dec. 31, 2030	Dec. 31, 2030	Dec. 31, 2030
Subsidiaries [Member] \| PRC Entities
Income Tax Examination [Line Items]
Effective income tax rate		25.00%
Subsidiaries [Member] \| Shanghai VIE
Income Tax Examination [Line Items]
Preferential tax rate percentage		15.00%
CAYMAN ISLANDS
Income Tax Examination [Line Items]
Taxable income				$ 0			$ 0			$ 0
Income tax expenses				$ 0			$ 0			$ 0
HONG KONG \| Subsidiaries [Member] \| Sunny Education (HK) Limited
Income Tax Examination [Line Items]
Taxable income					$ 0			$ 0			$ 0
Income tax expenses					$ 0			$ 0			$ 0
Assessable profit benchmark	$ 2,000,000
HONG KONG \| Subsidiaries [Member] \| Sunny Education (HK) Limited \| Minimum
Income Tax Examination [Line Items]
Effective income tax rate	8.25%
HONG KONG \| Subsidiaries [Member] \| Sunny Education (HK) Limited \| Maximum
Income Tax Examination [Line Items]
Effective income tax rate	16.50%

Income Taxes - Summary of Princ

Income Taxes - Summary of Principal Components of Deferred Taxes (Details) - CNY (¥) ¥ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Accrued expenses	¥ 12,142	¥ 9,231	¥ 7,242
Advertising expenses carrying forwards	24,202
Depreciation of property and equipment	388	853	1,318
Net operating loss carrying forwards	724,597	503,212	295,682
Total deferred tax assets	761,329	513,296	304,242
Less: valuation allowance	¥ (761,329)	¥ (513,296)	¥ (304,242)	¥ (177,785)

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Effective Tax Rate And Statutory Income Tax Rate (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Income Tax Disclosure [Abstract]
Loss before provision for income taxes	¥ (1,339,908)	$ (205,349)	¥ (963,750)	¥ (656,071)
Income tax benefit computed at an applicable tax rate of 25%	(334,977)		(240,938)	(164,018)
Effect of non-deductible expenses	11,540		3,738	2,821
Effect of research and development expenses super deduction	(24,037)		(10,740)	(2,361)
Effect of preferential tax rate	18,513		18,413	6,988
Effect on tax rates in different tax jurisdictions	80,928		20,473	30,113
Change in valuation allowance	248,033		209,054	126,457
Income tax expense

Income Taxes - Summary of Rec_2

Income Taxes - Summary of Reconciliation of Effective Tax Rate And Statutory Income Tax Rate (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020
PRC Entities
Income Tax Examination [Line Items]
Percentage of PRC income tax	25.00%

Income Taxes - Schedule of Move

Income Taxes - Schedule of Movements of Valuation Allowance (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of the period	¥ 513,296	¥ 304,242	¥ 177,785
Additions	248,033	209,054	126,457
Balance at end of the period	¥ 761,329	¥ 513,296	¥ 304,242

Ordinary Shares and Series A _2

Ordinary Shares and Series A Convertible Preferred Shares - Additional Information (Details) $ / shares in Units, ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019$ / sharesshares
Class Of Stock [Line Items]
Common stock, shares authorized			509,631,372
Common stock, par value \| $ / shares		$ 0.0001	$ 0.0001
Common stock, shares issued			57,864,058
Common stock, shares outstanding			57,864,058
Proceeds from the IPO and from exercising the over-allotment option by the underwriters	¥ 2,051,695	$ 314,436
Issuance cost \| ¥	¥ 28,153
Convertible preferred stock, terms of conversion	Each holder of convertible redeemable preferred shares shall have the right, at such holder's sole discretion, to convert all or any portion of the preferred shares into ordinary shares on a one-for-one basis at any time. The initial conversion price is the issuance price of preferred shares, subject to adjustment in the event of (1) share dividends, subdivisions, combinations or consolidation of ordinary shares, (2) reclassification, exchange and substitution, and (3) issuance of new securities at a price per share less than the applicable conversion price in effect on the date of and immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance.	Each holder of convertible redeemable preferred shares shall have the right, at such holder's sole discretion, to convert all or any portion of the preferred shares into ordinary shares on a one-for-one basis at any time. The initial conversion price is the issuance price of preferred shares, subject to adjustment in the event of (1) share dividends, subdivisions, combinations or consolidation of ordinary shares, (2) reclassification, exchange and substitution, and (3) issuance of new securities at a price per share less than the applicable conversion price in effect on the date of and immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance.
IPO
Class Of Stock [Line Items]
Proceeds from the IPO and from exercising the over-allotment option by the underwriters \| ¥	¥ 2,023,593
Issuance cost \| ¥	¥ 28,153
Ordinary Shares
Class Of Stock [Line Items]
Common stock, shares authorized			509,631,372
Common stock, par value \| $ / shares			$ 0.0001
Common stock, shares issued			57,864,058
Common stock, shares outstanding			57,864,058
Ordinary Shares \| IPO
Class Of Stock [Line Items]
Common stock, shares outstanding		77,884,733
American Depositary Shares \| IPO
Class Of Stock [Line Items]
Issuance of shares upon initial public offering	31,510,000	31,510,000
Class A Ordinary Shares \| IPO
Class Of Stock [Line Items]
Common stock, shares outstanding		27,867,521
Issuance of shares upon initial public offering	78,775,000	78,775,000
Class B Ordinary Shares \| IPO
Class Of Stock [Line Items]
Common stock, shares outstanding		50,017,212

Net Loss Per Share - Computatio

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Details) ¥ / shares in Units, $ / shares in Units, ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)¥ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019CNY (¥)¥ / sharesshares	Dec. 31, 2018CNY (¥)¥ / sharesshares
Net Income Loss Available To Common Stockholders Diluted [Abstract]
Net loss attributable to ordinary shareholders	¥ (4,177,899)	$ (640,290)	¥ (1,564,285)	¥ (900,442)
Weighted average ordinary shares outstanding used in computing basic and diluted net loss per share	93,503,437	93,503,437	57,410,827	48,676,298
Basic and diluted loss per share \| (per share)	¥ (44.68)	$ (6.85)	¥ (27.25)	¥ (18.50)

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Shares Outstanding Excluded from Calculation of Diluted Net Loss Per Ordinary Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares Issuable Upon Exercise of Share Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share	55,825,379	69,409,835	55,957,332
Shares Issuable Upon Vesting of Restricted Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share	9,272,591	423,804	12,914,110
Shares Issuable Upon Conversion of Series A Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		17,085,275	17,085,275
Shares Issuable Upon Conversion of Series B Convertible Redeemable Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		34,544,762	34,544,762
Shares Issuable Upon Conversion of Series B+ Convertible Redeemable Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		54,083,288	54,083,288
Shares Issuable Upon Conversion of Series C Convertible Redeemable Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		50,195,203	50,195,203
Shares Issuable Upon Conversion of Series D Convertible Redeemable Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		50,193,243	50,193,243
Shares Issuable Upon Conversion of Series E Convertible Redeemable Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		78,824,567	76,449,032
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares outstanding excluded from calculation of diluted net loss per ordinary share		4,959

Employee Defined Contribution_2

Employee Defined Contribution Plan - Additional Information (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Employee benefits, expense	¥ 100,957	¥ 132,728	¥ 99,720

Related Party Transaction - Sum

Related Party Transaction - Summary of Significant Balances Between Group and Related Party (Details) ¥ in Thousands	Dec. 31, 2019CNY (¥)
Related Party Transaction [Line Items]
Amounts due from related party	¥ 2,611
Fluency Holding Ltd.
Related Party Transaction [Line Items]
Amounts due from related party	¥ 2,611

Related Party Transaction - Add

Related Party Transaction - Additional Information (Details) ¥ in Thousands	1 Months Ended
	Sep. 30, 2020CNY (¥)shares	Jun. 30, 2020CNY (¥)Operation
Fluency Holding Ltd.
Related Party Transaction [Line Items]
Stock repurchase program number of shares authorized to be repurchased \| shares	115,324
Mr. Dun XIAO
Related Party Transaction [Line Items]
Equity method investment ownership percentage		100.00%
Loan receivable from related party		¥ 589
Consideration transferred	¥ 411	¥ 1,000
Substantial operation of the entity \| Operation		0

Segment Information - Additiona

Segment Information - Additional Information (Details)	12 Months Ended
Segment Information - Additional Information (Details)	Dec. 31, 2020Segment
Segment Reporting [Abstract]
Number of operating segment	1
Number of reporting segment	1

Restricted Net Assets - Additio

Restricted Net Assets - Additional Information (Details) - CNY (¥)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statutory Accounting Practices [Line Items]
Statutory capital and surplus required	¥ 2,632,554	¥ 1,602,510
Wholly-owned Foreign Invested Enterprise
Statutory Accounting Practices [Line Items]
Appropriation of after tax profit to statutory common reserve limit registered capital percentage	50.00%
Wholly-owned Foreign Invested Enterprise \| Minimum
Statutory Accounting Practices [Line Items]
Appropriation of after tax profit to statutory common reserve required minimum percentage	10.00%
Domestic Enterprise
Statutory Accounting Practices [Line Items]
Appropriation of after tax profit to statutory common reserve limit registered capital percentage	50.00%
Domestic Enterprise \| Minimum
Statutory Accounting Practices [Line Items]
Appropriation of after tax profit to statutory common reserve required minimum percentage	10.00%

Financial Statement Schedule I

Financial Statement Schedule I Condensed Financial Information of Parent Company Balance Sheets (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)	Dec. 31, 2017CNY (¥)
Current assets
Cash and cash equivalents	¥ 2,834,962	$ 434,477	¥ 653,859	¥ 1,252,983
Amounts due from a related party			2,611
Total current assets	3,046,580	466,909	757,624
TOTAL ASSETS	3,389,742	519,500	918,289
Current liabilities
Accrued expenses and other current liabilities	539,787	82,725	309,031
Total current liabilities	1,205,503	184,750	680,704
Non-current liabilities
TOTAL LIABILITIES	1,325,592	203,155	702,638
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			4,675,579
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares			37
Additional paid-in capital	10,653,403	1,632,705
Accumulated other comprehensive income	49,614	7,604	88,216
Accumulated deficit	(8,639,180)	(1,324,012)	(4,602,437)
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	2,064,150	316,345	(4,459,928)	¥ (2,976,214)	¥ (2,256,992)
TOTAL LIABILITIES, MEZZANINE EQUITY AND SHAREHOLDERS' (DEFICIT) EQUITY	3,389,742	519,500	918,289
Series B Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			330,817
Series B+ Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			516,469
Series C Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			504,721
Series D Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			1,227,905
Series E Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			2,095,667
Class A Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	275	42
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	275	42
Class B Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	38	6
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	38	6
Series A Convertible Preferred Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Series A convertible preferred shares (US$0.0001 par value; 22,257,215 and nil shares authorized as of December 31, 2019 and 2020, respectively, 17,085,275 and nil issued and outstanding as of December 31, 2019 and 2020, respectively)			54,256
Parent Company
Current assets
Cash and cash equivalents	2,108,582	323,154	290,578
Amounts due from subsidiaries	716,696	109,838	771,355
Amounts due from a related party			2,611
Total current assets	2,825,278	432,992	1,064,544
TOTAL ASSETS	2,825,278	432,992	1,064,544
Current liabilities
Accrued expenses and other current liabilities	3,768	577	2,207
Total current liabilities	3,768	577	2,207
Non-current liabilities
Deficits of investments in subsidiaries, VIEs and VIEs' subsidiaries	757,360	116,070	846,686
Total non-current liabilities	757,360	116,070	846,686
TOTAL LIABILITIES	761,128	116,647	848,893
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			4,675,579
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares			37
Additional paid-in capital	10,653,403	1,632,705
Accumulated other comprehensive income	49,614	7,604	88,216
Accumulated deficit	(8,639,180)	(1,324,012)	(4,602,437)
TOTAL SHAREHOLDERS' (DEFICIT) EQUITY	2,064,150	316,345	(4,459,928)
TOTAL LIABILITIES, MEZZANINE EQUITY AND SHAREHOLDERS' (DEFICIT) EQUITY	2,825,278	432,992	1,064,544
Parent Company \| Series B Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			330,817
Parent Company \| Series B+ Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			516,469
Parent Company \| Series C Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			504,721
Parent Company \| Series D Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			1,227,905
Parent Company \| Series E Convertible Redeemable Preferred Shares
MEZZANINE EQUITY
TOTAL MEZZANINE EQUITY			2,095,667
Parent Company \| Class A Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	275	42
Parent Company \| Class B Ordinary Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Ordinary shares	¥ 38	$ 6
Parent Company \| Series A Convertible Preferred Shares
SHAREHOLDERS' (DEFICIT) EQUITY
Series A convertible preferred shares (US$0.0001 par value; 22,257,215 and nil shares authorized as of December 31, 2019 and 2020, respectively, 17,085,275 and nil issued and outstanding as of December 31, 2019 and 2020, respectively)			¥ 54,256

Financial Statement Schedule _2

Financial Statement Schedule I Condensed Financial Information of Parent Company Balance Sheets (Parenthetical) (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2018
Convertible redeemable preferred shares, shares issued	301,298,172
Convertible redeemable preferred shares, shares outstanding		267,841,063
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized		509,631,372
Common stock, shares issued		57,864,058
Common stock, shares outstanding		57,864,058
Series B Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized		34,815,112
Convertible redeemable preferred shares, shares issued	34,815,112	34,544,762
Convertible redeemable preferred shares, shares outstanding		34,544,762
Series B+ Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, shares issued	54,083,288
Convertible redeemable preferred shares, shares outstanding		54,083,288
Series C Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized		50,195,203
Convertible redeemable preferred shares, shares issued	50,195,203	50,195,203
Convertible redeemable preferred shares, shares outstanding		50,195,203
Series D Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized		50,193,243
Convertible redeemable preferred shares, shares issued	50,193,243	50,193,243
Convertible redeemable preferred shares, shares outstanding		50,193,243
Series E Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized		78,824,567
Convertible redeemable preferred shares, shares issued	78,824,567	78,824,567	78,824,567
Convertible redeemable preferred shares, shares outstanding		78,824,567
Class A Ordinary Shares
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,300,000,000
Common stock, shares issued	421,729,902
Common stock, shares outstanding	421,729,902
Class B Ordinary Shares
Common stock, par value	$ 0.0001	0.0001
Common stock, shares authorized	100,000,000
Common stock, shares issued	58,453,168
Common stock, shares outstanding	58,453,168
Series A Convertible Preferred Shares
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		22,257,215
Preferred stock, shares issued		17,085,275
Preferred stock, shares outstanding		17,085,275
Parent Company
Common stock, par value	0.0001	$ 0.0001
Common stock, shares authorized		509,631,372
Common stock, shares issued		57,864,058
Common stock, shares outstanding		57,864,058
Parent Company \| Series B Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized	34,815,112	34,815,112
Convertible redeemable preferred shares, shares issued	34,544,762	34,544,762
Convertible redeemable preferred shares, shares outstanding	34,544,762	34,544,762
Parent Company \| Series B+ Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized	54,083,288	54,083,288
Convertible redeemable preferred shares, shares issued	54,083,288	54,083,288
Convertible redeemable preferred shares, shares outstanding	54,083,288	54,083,288
Parent Company \| Series C Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized	50,195,203	50,195,203
Convertible redeemable preferred shares, shares issued	50,195,203	50,195,203
Convertible redeemable preferred shares, shares outstanding	50,195,203	50,195,203
Parent Company \| Series D Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized	50,193,243	50,193,243
Convertible redeemable preferred shares, shares issued	50,193,243	50,193,243
Convertible redeemable preferred shares, shares outstanding	50,193,243	50,193,243
Parent Company \| Series E Convertible Redeemable Preferred Shares
Convertible redeemable preferred shares, par value	$ 0.0001	$ 0.0001
Convertible redeemable preferred shares, shares authorized	78,824,567	78,824,567
Convertible redeemable preferred shares, shares issued	78,824,567	78,824,567
Convertible redeemable preferred shares, shares outstanding	78,824,567	78,824,567
Parent Company \| Class A Ordinary Shares
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,300,000,000
Common stock, shares issued	421,729,902
Common stock, shares outstanding	421,729,902
Parent Company \| Class B Ordinary Shares
Common stock, par value	$ 0.0001	0.0001
Common stock, shares authorized	100,000,000
Common stock, shares issued	58,453,168
Common stock, shares outstanding	58,453,168
Parent Company \| Series A Convertible Preferred Shares
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		22,257,215
Preferred stock, shares issued		17,085,275
Preferred stock, shares outstanding		17,085,275

Financial Statement Schedule _3

Financial Statement Schedule I Condensed Financial Information of Parent Company Statement of Operations (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Sales and marketing expenses	¥ (1,097,932)	$ (168,265)	¥ (583,818)	¥ (303,492)
Research and development expenses	(614,770)	(94,218)	(491,266)	(398,627)
General and administrative expenses	(420,114)	(64,385)	(157,793)	(203,129)
Total operating expenses	(2,132,816)	(326,868)	(1,232,877)	(905,248)
Loss from operations	(1,334,116)	(204,462)	(1,000,108)	(699,509)
Interest income	8,422	1,291	23,834	33,980
Foreign currency exchange (loss) gain	(15,557)	(2,384)	12,907	8,576
Loss before provision for income tax	(1,339,908)	(205,349)	(963,750)	(656,071)
Income tax expenses
Net loss	(1,339,908)	(205,349)	(963,750)	(656,071)
Accretion of convertible redeemable preferred shares	(2,837,991)	(434,941)	(600,535)	(244,371)
Net loss available to ordinary shareholders of 17 Education & Technology Group Inc.	(4,177,899)	(640,290)	(1,564,285)	(900,442)
Parent Company
Sales and marketing expenses	(35,077)	(5,376)	(8,737)	(15,965)
Research and development expenses	(68,688)	(10,527)	(22,933)	(12,254)
General and administrative expenses	(257,873)	(39,521)	(64,961)	(115,253)
Total operating expenses	(361,638)	(55,424)	(96,631)	(143,472)
Loss from operations	(361,638)	(55,424)	(96,631)	(143,472)
Interest income	1,045	160	13,642	25,088
Foreign currency exchange (loss) gain	1,699	260	(779)	(3,669)
Loss before provision for income tax	(358,894)	(55,004)	(83,768)	(122,053)
Loss from investment in subsidiaries	(981,014)	(150,345)	(879,982)	(534,018)
Net loss	(1,339,908)	(205,349)	(963,750)	(656,071)
Accretion of convertible redeemable preferred shares	(2,837,991)	(434,941)	(600,535)	(244,371)
Net loss available to ordinary shareholders of 17 Education & Technology Group Inc.	¥ (4,177,899)	$ (640,290)	¥ (1,564,285)	¥ (900,442)

Financial Statement Schedule _4

Financial Statement Schedule I Condensed Financial Information of Parent Company Consolidated Statements of Comprehensive Income (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Net loss	¥ (1,339,908)	$ (205,349)	¥ (963,750)	¥ (656,071)
Other comprehensive income (loss), net of tax of nil:
Change in cumulative foreign currency translation adjustments	(38,602)	(5,916)	(11,972)	69,566
Total comprehensive loss attributable to 17 Education & Technology Group Inc.	(1,378,510)	(211,265)	(975,722)	(586,505)
Parent Company
Net loss	(1,339,908)	(205,349)	(963,750)	(656,071)
Other comprehensive income (loss), net of tax of nil:
Change in cumulative foreign currency translation adjustments	(38,602)	(5,916)	(11,972)	69,566
Total comprehensive loss attributable to 17 Education & Technology Group Inc.	¥ (1,378,510)	$ (211,265)	¥ (975,722)	¥ (586,505)

Financial Statement Schedule _5

Financial Statement Schedule I Condensed Financial Information of Parent Company Statement of Cash Flows (Details) ¥ in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2020CNY (¥)	Jun. 30, 2020USD ($)	Dec. 31, 2020CNY (¥)	Dec. 31, 2020USD ($)	Dec. 31, 2019CNY (¥)	Dec. 31, 2018CNY (¥)
Net cash generated from (used in) operating activities			¥ (522,988)	$ (80,150)	¥ (631,288)	¥ (418,865)
CASH FLOWS FROM INVESTING ACTIVITIES
Net cash used in investing activities			(89,504)	(13,717)	(28,594)	(48,947)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the IPO and from exercising the over-allotment option by the underwriters			2,051,695	314,436
Payment of the IPO issuance cost			(18,469)	(2,830)
Payment to repurchase of ordinary shares						(21,082)
Payment to repurchase of the Series A convertible preferred shares						(4,730)
Repurchase and cancellation of vested options			(528)	(81)	(551)	(11,883)
Net proceeds from the issuance of convertible redeemable preferred shares			3,274,069			1,588,067
Net cash generated from financing activities			2,797,421	428,724	84,449	1,550,372
Net increase (decrease) in cash and cash equivalents and restricted cash			2,146,430	328,955	(587,142)	1,155,363
Cash, cash equivalents and restricted cash at beginning of the year			688,702	105,548	1,275,844	120,481
Cash, cash equivalents and restricted cash at end of the year			2,835,132	434,503	688,702	1,275,844
Series F Convertible Redeemable Preferred Shares
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from the issuance of convertible redeemable preferred shares	¥ 849,528	$ 120,000	849,528	130,196
Parent Company
Net cash generated from (used in) operating activities			(4,214)	(646)	11,529	1,477
CASH FLOWS FROM INVESTING ACTIVITIES
Amounts due from subsidiaries					(60,137)	(142,237)
Investments in subsidiaries			(1,024,607)	(157,028)	(671,566)	(539,608)
Net cash used in investing activities			(1,024,607)	(157,028)	(731,703)	(681,845)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the IPO and from exercising the over-allotment option by the underwriters			2,051,695	314,436
Payment of the IPO issuance cost			(18,469)	(2,830)
Payment to repurchase of ordinary shares						(21,082)
Payment to repurchase of the Series A convertible preferred shares						(4,730)
Repurchase and cancellation of vested options			(528)	(81)	(551)	(11,883)
Net proceeds from the issuance of convertible redeemable preferred shares						1,588,067
Net cash generated from financing activities			2,882,226	441,721	(551)	1,550,372
Effect of exchange rate changes			(35,401)	(5,426)	(1,536)	114,770
Net increase (decrease) in cash and cash equivalents and restricted cash			1,818,004	278,621	(722,261)	984,774
Cash, cash equivalents and restricted cash at beginning of the year			290,578	44,533	1,012,839	28,065
Cash, cash equivalents and restricted cash at end of the year			2,108,582	323,154	¥ 290,578	¥ 1,012,839
Parent Company \| Series F Convertible Redeemable Preferred Shares
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from the issuance of convertible redeemable preferred shares			¥ 849,528	$ 130,196

Financial Statement Schedule _6

Financial Statement Schedule I Condensed Financial Information of Parent Company Statement of Cash Flows (Parenthetical) (Details) ¥ in Thousands	12 Months Ended
	Dec. 31, 2020CNY (¥)
Issuance cost of redeemable preferred shares	¥ 15,770
Parent Company \| Series E Convertible Redeemable Preferred Shares
Issuance cost of redeemable preferred shares	¥ 15,770

Financial Statement Schedule _7

Financial Statement Schedule I Condensed Financial Information of Parent Company - Convenience Translation - Additional Information (Details)	Dec. 31, 2020
Additional Financial Statement Information [Line Items]
USD exchange rate	6.5250
Parent Company
Additional Financial Statement Information [Line Items]
USD exchange rate	6.5250