Massmutual Premier Funds N-CSRCertified annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Item 1. Reports to Stockholders.

This material must be preceded or accompanied by a current prospectus (or summary prospectus, if available) for the applicable MassMutual Funds. Investors should consider a Fund’s investment objective, risks, and charges and expenses carefully before investing. This and other information about the investment company is available in the prospectus (or summary prospectus, if available). Read it carefully before investing.

[THIS PAGE INTENTIONALLY LEFT BLANK]

September 30, 2023

Global markets continue to reward retirement investors

During the fiscal year ended September 30, 2023, U.S. stocks were up over 21%, in a market environment where the U.S. Federal Reserve (the “Fed”) raised interest rates by nearly 3% in an effort to combat heightened inflation by curtailing economic activity. Stocks in foreign developed markets and emerging markets also experienced significant gains during the fiscal year, aided by a weaker U.S. dollar. Global stock gains during the period were driven by a resilient consumer, surprisingly strong economic activity, strong suggestions of a generative artificial intelligence (“AI”) revolution, and investors’ improving earnings expectations. U.S. bond investors experienced slightly positive returns in the rising interest rate environment, fueled by aggressive interest rate hikes by the Fed that were aimed at reducing demand-driven inflationary pressures.

Market highlights

Market environment

For the fiscal year beginning on October 1, 2022, global stock investors experienced significant gains. During this period, U.S. stock prices rose sharply in response, with the S&P 500 Index^® (“S&P 500”)¹ entering bull market territory after rising more than 20% from its previous highs. Investors breathed a sigh of relief as the possibility of a recession lessened in the face of robust economic activity and falling inflation during the period. Consumer sentiment rose sharply, up 19.4% in the period,² aided by lower inflation, low unemployment, and positive wage growth. In MassMutual’s view, the strong economic growth may be unsustainable, as more Americans are borrowing to make ends meet, resulting in consumer loan levels at record highs, having increased by 5.8% year-over-year.³

¹ The S&P 500 Index measures the performance of 500 widely held stocks in the U.S. equity market. Standard and Poor’s chooses member companies for the Index based on market size, liquidity, and industry group representation. Included are the stocks of industrial, financial, utility, and transportation companies. Since mid-1989, this composition has been more flexible and the number of issues in each sector has varied. The Index is market capitalization-weighted. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

² August 2023, University of Michigan: Consumer Sentiment (UMCSENT), retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/UMCSENT, October 5, 2023.

³ August 2023, Board of Governors of the Federal Reserve System (US), Consumer Loans, All Commercial Banks [CONSUMER], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/CONSUMER, October 5, 2023.

1

As a result, the broad-market S&P 500 rose 21.62% for the period. The technology-heavy NASDAQ Composite Index⁴ performed even better, rising 26.11% for the period. The more economically sensitive Dow Jones Industrial Average^SM5 was up 19.18% for the period. During the reporting period, small-cap stocks underperformed their larger-cap peers, while growth stocks outperformed their value brethren. The information technology and communication services sectors were each up by 35% or more for the period. The utilities sector was the weakest performer for the fiscal year, down 7.02% over the period, hurt by the sharp rise in interest rates that made the stock dividend yields less attractive. The real estate sector also ended the period in the red, declining 1.84%.

Developed international markets, as measured by the MSCI EAFE^® Index,⁶ outperformed their domestic peers, ending the fiscal year up 25.65%. Emerging-market stocks, as measured by the MSCI Emerging Markets Index,⁷ also rose sharply, ending up 11.70% for the period. Investors shifted back into developed international and emerging-market stocks during the period in response to lower-than-expected energy costs, a more resilient consumer, and stronger-than-expected economic activity.

Bond yields rose sharply during the fiscal year, with the 10-year U.S. Treasury bond yield rising from 3.83% on October 1, 2022 to close the period at 4.59%. During the period, rising yields produced falling bond prices, and bond index returns suffered. The Bloomberg U.S. Aggregate Bond Index⁸ ended the period up 0.64%. Investment-grade corporate bonds fared better. The Bloomberg U.S. Corporate Bond Index,⁹ which tracks investment-grade corporate bonds, ended the period with a 3.65% gain. The Bloomberg U.S. Corporate High-Yield Bond Index¹⁰ also ended the period higher, rising 10.28%.

Review and maintain your strategy

At MassMutual, looking out for each other isn’t just a nice idea; it’s how we’ve done business for more than 170 years. Since 1851, we’ve had a single purpose: to help people secure their future and protect the ones they love. While the current market volatility, including the reality of market sell-offs, can test an investor’s mettle, we’d like to remind you that, as a retirement investor, it’s important to maintain perspective and have realistic expectations about the future performance of your investment accounts. As described in this report, financial markets can reverse suddenly, with little or no notice. That’s why we continue to believe that retirement investors should create and maintain a plan that focuses on their goals, how long they have to invest, and how comfortable they are with market volatility. Our multi-managed and sub-advised mutual funds tap into the deep expertise

⁴ The NASDAQ Composite Index measures the performance of all domestic and international based common type stocks listed on the NASDAQ Stock Market. It includes common stocks, ordinary shares, ADRs, shares of beneficial interest or limited partnership interests, and tracking stocks. The Index is market capitalization-weighted. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

⁵ The Dow Jones Industrial Average Index measures the performance of stocks of 30 U.S. blue-chip companies covering all industries with the exception of transportation and utilities. It is price-weighted. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

⁶ The MSCI EAFE Index measures the performance of the large- and mid-cap segments of developed markets, excluding the U.S. and Canada equity securities. It is free float-adjusted market-capitalization weighted. The Index does not reflect any deduction for fees or expenses and cannot be purchased directly by investors.

⁷ The MSCI Emerging Markets Index measures the performance of the large- and mid-cap segments of emerging market equity securities. It is free float-adjusted market-capitalization weighted. The Index does not reflect any deduction for fees or expenses and cannot be purchased directly by investors.

⁸ The Bloomberg U.S. Aggregate Bond Index measures the performance of investment grade, U.S. dollar-denominated, fixed-rate taxable bond market securities, including Treasuries, government-related and corporate securities, mortgage-backed securities (MBS) (agency fixed-rate and hybrid ARM pass-throughs), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS). It rolls up into other Bloomberg flagship indexes, such as the multi-currency Global Aggregate Index and the U.S. Universal Index, which includes high yield and emerging markets debt. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

⁹ The Bloomberg U.S. Corporate Bond Index measures the performance of the investment grade, U.S. dollar-denominated, fixed-rate, taxable corporate bond market. It includes U.S. dollar-denominated securities publicly issued by U.S. and non-U.S. industrial, utility, and financial issuers that meet specified maturity, liquidity, and quality requirements. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

¹⁰ The Bloomberg U.S. Corporate High-Yield Bond Index measures the performance of U.S. dollar-denominated, non-investment grade, fixed-rate, taxable corporate bonds, including corporate bonds, fixed-rate bullet, putable, and callable bonds, SEC Rule 144A securities, original issue zeros, pay-in-kind bonds, fixed-rate and fixed-to-floating capital securities. The Index does not reflect any deduction for fees, expenses, or taxes and cannot be purchased directly by investors.

2

of seasoned asset managers who are committed to helping long-term investors prepare for retirement – in all market conditions. As always, we recommend that you work with a personal financial professional, who can help you define an investment strategy that aligns with your comfort level with respect to market volatility, how long you have to save and invest, and your specific financial goals. Thank you for your confidence in MassMutual.

The information provided is the opinion of MML Investment Advisers, LLC (“MML Advisers”) and is subject to change without notice. It is not to be construed as tax, legal, or investment advice. Of course, past performance does not guarantee future results.

Underwriter: MML Distributors, LLC (MMLD), Member FINRA and SIPC (www.FINRA.org and www.SIPC.org), 1295 State Street, Springfield, MA 01111-0001. Investment advisory services are provided to the Funds by MML Advisers. MMLD and MML Advisers are subsidiaries of MassMutual.

^©2023 Massachusetts Mutual Life Insurance Company (MassMutual^®), Springfield, MA 01111-0001. All rights reserved. www.MassMutual.com.

3

What is the investment approach of MassMutual U.S. Government Money Market Fund, and who is the Fund’s subadviser?

The Fund seeks current income consistent with preservation of capital and liquidity. The Fund normally invests at least 99.5% of its total assets in cash, U.S. Government securities, and/or repurchase agreements fully collateralized by cash or U.S. Government securities. Under normal circumstances, the Fund invests at least 80% of its net assets in U.S. Government securities and repurchase agreements that are fully collateralized by U.S. Government securities. The Fund’s subadviser is Barings LLC (Barings). The Fund seeks to maintain, but does not guarantee, a stable $1.00 share price. You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 4.08%, underperforming the 4.71% return of the FTSE 3-Month U.S. T Bill Index (the “benchmark”), which measures the performance of the last three three-month Treasury bill month-end rates.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

During the fiscal year ended September 30, 2023, the U.S. Federal Reserve (the “Fed”) continued its most aggressive rate hiking cycle in many decades, raising the federal funds rate – the Fed’s overnight bank lending rate – to a range from 3.00%-3.25% to 5.25%-5.50% over the course of the fiscal year in an effort to combat inflation that, as of the end of the period, was slowing, but still well above the Fed’s stated goal. At this time one year ago, the market was generally pricing in an additional 1.25% of tightening in the year ahead, and then many in the market generally assumed the Fed would start cutting rates during the third quarter of 2023. The economy has been more resilient than the market originally expected, with sticky inflation and stronger-than-expected employment numbers. Consequently, as of the end of the fiscal period, the federal funds rate sat 1.00% higher than what was originally forecasted. This entire lending rate cycle yielded higher rates than market participants generally expected during the period.

The larger-than-expected increase in Secured Overnight Financing Rates (“SOFR”) throughout the fiscal year had a positive effect on performance, as the Fund continued to own a large of amount of floating-rate paper and kept its weighted average maturity (“WAM”) in single digits for more than half of the fiscal year. (SOFR is a broad measure of the cost of borrowing cash overnight collateralized by Treasury securities.) As of the end of the period, the Fund’s current exposure to floating-rate paper was 49%, compared to 68% at the end of the previous fiscal year.

The Fund stayed short with its fixed-rate purchases throughout the fiscal year, as the curve out to one year was very flat and provided little incremental yield pickup. The yield curve is a graph showing the term structure of interest rates by plotting the yields of all bonds of comparable quality with maturities ranging from the shortest – typically one month – to the longest – typically 30 years – available. The resulting curve shows whether short-term interest rates are higher or lower than long-term rates. Additionally, the Fund’s lack of access to the Fed’s reverse repo program detracted from the Fund’s performance during the period. In Barings’ experience, the flatness of the curve and the lack of any credit exposure typically make it difficult to pick up extra yield in a government-only fund.

Subadviser outlook

In Barings’ observation, Fed Chair Powell and other Federal Open Market Committee (“FOMC”) members have generally consistently maintained their hawkish rhetoric, even as inflation numbers have cooled down throughout the first three quarters of 2023. As of the end of the period, the market was a little more skeptical that the Fed will actually follow through on their hawkish comments. Regardless of whether the Fed is done hiking interest rates or if they end up further hiking rates, Barings believes that the market is in the last innings of this tightening rate cycle. Barings believes that the biggest question in the coming

4

fiscal year is whether the Fed can engineer a soft landing – or if the U.S. will slide into a recession. In Barings’ view, a recession would likely mean that the Fed would start easing rates sooner, whereas a soft landing could entail the Fed maintaining higher rates for a longer period of time. Barings expects that the Fund will look to buy more fixed-rate securities and increase its WAM in the next fiscal year. The WAM of the Fund has been at very low levels for the last 18 months and, in Barings’ opinion, that has worked very well. However, in the coming fiscal year, Fund management expects to begin the process of repositioning the Fund’s holdings. During this time, Barings plans to monitor Fed language carefully and act accordingly if they see signs of policy changing. Moreover, Barings believes that the new money market rules affecting liquidity requirements may have a negative effect on the Fund’s performance in the future.

5

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

6

What is the investment approach of MassMutual Short-Duration Bond Fund, and who is the Fund’s subadviser?

The Fund seeks to achieve a high total rate of return primarily from current income while minimizing fluctuations in capital values by investing primarily in a diversified portfolio of short-term investment grade fixed income securities. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in investment grade fixed income securities (rated Baa3 or higher by Moody’s, BBB- or higher by Standard & Poor’s or the equivalent by any nationally recognized statistical rating organization, or, if unrated, determined to be of comparable quality by the Fund’s subadviser or sub-subadviser). The Fund’s subadviser is Barings LLC (Barings). In addition, Baring International Investment Limited serves as a sub-subadviser for the Fund.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 3.71%, outperforming the 2.80% return of the Bloomberg U.S. Aggregate 1-3 Year Bond Index (the “benchmark”), which measures the performance of investment grade, U.S. dollar-denominated, fixed-rate taxable bond market securities with maturities of 1-3 years, including Treasuries, government-related and corporate securities, mortgage-backed securities (MBS) (agency fixed-rate and hybrid ARM pass-throughs), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS). (“Agency” refers to debt issued by U.S. federal government agencies or government-sponsored entities for financing purposes.)

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, the front end of the U.S. Treasury curve remained elevated as a result of interest rate hikes from the U.S Federal Reserve (the “Fed”). The yield curve is a graph showing the term structure of interest rates by plotting the yields of all bonds of comparable quality with maturities ranging from the shortest – typically one month – to the longest – typically 30 years – available. The resulting curve shows whether short-term interest rates are higher or lower than long-term rates.

The Fund managed interest rate exposure to match that of the benchmark starting in the third quarter of 2023. The effective duration of the Fund finished the period at 1.77 years. The duration positioning of the Fund contributed positively to performance over the period. Duration is a measure of a bond fund’s sensitivity to interest rates. The longer the duration, the greater the price impact on the bond or portfolio when interest rates rise or fall. An underweight allocation to U.S. Treasuries, relative to the benchmark, contributed positively to the Fund’s relative performance over the period.

The Fund’s overweight allocation to investment-grade corporates contributed positively to performance, whereas its allocation to BB-rated high-yield corporates detracted. Banks, brokers, food, beverage, tobacco, and real estate investment trusts (REITs) were among the top-performing industry holdings. Other-finance, property & casualty insurance, and technology were among the Fund’s top-detracting industry holdings. During the period, the Fund favored industries less susceptible to merger and acquisition (M&A) risk, such as banking and diversified industrial industries.

ABS contributed positively to performance over the period. The Fund held an overweight allocation the sector. During a majority of the period, the asset class saw significant spread widening as a result of the market’s risk off tone amid the backdrop of increased rate volatility; however, the third quarter of 2023 showed a reversal of this trend. Spreads represent the difference in yields between comparable Treasury and corporate bonds. Tightening spreads often reflect rising corporate bond prices; widening spreads often reflect falling corporate bond prices. Over the third quarter of 2023, the ABS market remained mostly firm, with some sectors showing marginal tightening. CMBS and residential mortgage-backed securities (RMBS) both detracted from relative performance over the period. The Fund finished the period with overweight allocations to these two sectors. The Fund’s allocation to MBS detracted slightly from relative performance.

7

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both. The Fund uses derivative instruments on occasion for yield curve, duration, downside risk management and to gain exposures. The use of derivatives detracted from performance over the period.

Subadviser outlook

In Barings’ observation, Fed Chair Powell and other Federal Open Market Committee (“FOMC”) members have generally consistently maintained their hawkish rhetoric, even as inflation numbers have cooled down throughout the first three quarters of 2023. As of the end of the period, the market was a little more skeptical that the Fed will actually follow through on their hawkish comments. Regardless of whether the Fed is done hiking interest rates or if they end up further hiking rates, Barings believes that the market is in the last innings of this tightening rate cycle. Barings believes that the biggest question in the coming fiscal year is whether the Fed can engineer a soft landing – or if the U.S. will slide into a recession. In Barings’ view, a recession would likely mean that the Fed would start easing rates sooner, whereas a soft landing could entail the Fed maintaining higher rates for a longer period of time. During this time, Barings plans to monitor Fed language carefully and act accordingly if they see signs of policy changing.

8

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

9

What is the investment approach of MassMutual Inflation-Protected and Income Fund, and who is the Fund’s subadviser?

The Fund seeks to achieve as high a total rate of real return on an annual basis as is considered consistent with prudent investment risk and the preservation of capital by investing, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in inflation-indexed bonds and other income-producing securities. The Fund’s subadviser is Barings LLC (Barings). In addition, Baring International Investment Limited serves as a sub-subadviser for the Fund.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 1.56%, outperforming the 1.25% return of the Bloomberg U.S. Treasury Inflation Protected Securities (TIPS) Index (Series-L) (the “benchmark”), which measures the performance of rules-based, market value-weighted inflation-protected securities issued by the U.S. Treasury. It is a subset of the Global Inflation-Linked Index (Series-L).

How do inflation-indexed bonds protect against inflation?

Like many other fixed-income securities, inflation-indexed bonds pay income twice a year, based on a stated coupon rate. However, both the principal and the interest payment are adjusted for the level of inflation. The inflation rate – as measured by the Consumer Price Index for All Urban Consumers (“CPI-U”) – results in an adjustment to the principal amount of an inflation-protected security. The coupon rate is then applied to the adjusted principal amount to determine the interest payment. For example, assuming an inflation rate of 3%, a security with a par value of $1,000 and an annual coupon rate of 1.75%, the adjusted principal amount after one year would be $1,030 ($1,000 increased by 3%). The semi-annual interest payment would be calculated by multiplying $1,030 by 1.75% and dividing by 2 instead of using the original $1,000 par value to calculate the amount of interest.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

Consumer prices, as measured by the U.S. Bureau of Labor Statistics (BLS), were down for the fiscal year ended September 30, 2023, as unadjusted Headline CPI came in at 3.7% for the month of August, down from 6.5% at year-end 2022. Core CPI (excluding energy and food prices) decreased to 4.3% for the month of August, down from 5.7% at year-end 2022. As of the end of the Fund’s fiscal year, core CPI was running well above the 2% inflation objective of the Federal Open Market Committee (FOMC).

TIPS positioning in aggregate marginally contributed to the Fund’s performance during the period. A small allocation to high-quality income-producing assets detracted.

In addition to TIPS, the Fund also invested in high-quality income-producing securities during the period, including asset-backed and money market securities. The income earned by these asset classes contributed positively over the fiscal year. The Fund’s allocation to asset-backed securities was the main driver of performance. Security selection in auto loans and insurance receivables within the asset-backed securities (ABS) sector were the primary contributors. Allocations to residential mortgage-backed securities (RMBS) also substantially contributed to performance.

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both. The Fund may use derivative instruments for yield curve and duration management, as well as for replicating cash bonds and gaining market exposure to implement manager views. The yield curve is a graph showing the term structure of interest rates by plotting the yields of all bonds of comparable quality with maturities ranging from the shortest – typically one month – to the longest – typically 30 years – available. The resulting curve shows whether short-term interest rates are higher or lower than long-term rates. Duration is a measure of a bond fund’s sensitivity to interest rates. The longer the duration, the greater the price impact on the bond or portfolio when interest rates rise or fall. During the reporting period, the Fund’s use of derivatives contributed to performance.

10

Subadviser outlook

Barings notes that although the Federal Reserve (Fed) decided to leave its benchmark interest rate unchanged in September, the Fed also signaled that borrowing costs will likely remain higher for a longer period after one more rate hike in calendar year 2023. The FOMC stated that they will determine the extent of additional policy firming that may be appropriate. Fed Chair Jerome Powell also mentioned that the Fed is prepared to raise rates further if necessary and will maintain policy at a restrictive level until they are confident that inflation is moving down sustainably. The FOMC’s quarterly projections indicate that 12 out of 19 officials support another rate hike in calendar year 2023 to support continued deceleration of inflation. Given the current market volatility as of the end of the fiscal period, the Fund has been positioned close to the duration of the benchmark. Fund management believes inflation expectations could continue to moderate as the Fed actions transmit through the economy in the coming months.

11

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

12

What is the investment approach of MassMutual Core Bond Fund, and who is the Fund’s subadviser?

The Fund seeks to achieve a high total rate of return consistent with prudent investment risk and the preservation of capital by investing primarily in a diversified portfolio of investment grade fixed income securities. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in investment grade fixed income securities (rated Baa3 or higher by Moody’s, BBB- or higher by Standard & Poor’s or the equivalent by any nationally recognized statistical rating organization, or, if unrated, determined to be of comparable quality by the Fund’s subadviser or sub-subadviser). The Fund’s portfolio dollar-weighted average duration generally matches (within 10%) the average duration of the Bloomberg U.S. Aggregate Bond Index. The Fund’s subadviser is Barings LLC (Barings). In addition, Baring International Investment Limited serves as a sub-subadviser for the Fund.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 0.91%, outperforming the 0.64% return of the Bloomberg U.S. Aggregate Bond Index (the “benchmark”), which measures the performance of investment grade, U.S. dollar-denominated, fixed-rate taxable bond market securities, including Treasuries, government-related and corporate securities, mortgage-backed securities (MBS) (agency fixed-rate and hybrid ARM pass-throughs), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS). (“Agency” refers to debt issued by U.S. federal government agencies or government-sponsored entities for financing purposes.)

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, the Fund’s overweight allocation, relative to the benchmark, to investment-grade corporate credit contributed positively to performance, while the Fund’s overweight allocation to high-yield corporates detracted slightly. Investments in other-finance, midstream/pipes, and life insurance were among the Fund’s top-performing industry positions. Conversely, the Fund’s technology, retail, restaurant, supermarket, and health insurance industry positions were among the top detracting corporate positions over the period.

ABS, where the Fund held an overweight allocation, was a marginally positive contributor to returns during the fiscal year. During a majority of the period, the asset class saw significant spread widening as a result of the market’s risk off tone amid the backdrop of increased rate volatility; however, the third quarter of 2023 showed a reversal of this trend. (Spreads represent the difference in yields between comparable Treasury and corporate bonds. Tightening spreads often reflect rising corporate bond prices; widening spreads often reflect falling corporate bond prices.) Over the third quarter of 2023, the ABS market remained mostly firm, with some sectors showing marginal tightening.

CMBS and residential mortgage-backed securities (RMBS) both detracted from relative performance over the period. The Fund finished the period with overweight positions in these two sectors. The Fund’s allocation to MBS contributed positively to performance. An allocation to high-quality short-weighted average life collateralized loan obligations (CLOs) detracted from performance. On the other hand, the Fund’s underweight allocation to Treasuries contributed positively to returns over the period.

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both. The Fund uses derivative instruments for yield curve, duration, downside hedging, and to gain exposures. They may also be used as a substitute as a direct investment. In aggregate, the Fund’s derivatives positions detracted from performance over the reporting period.

Subadviser outlook

In Barings’ observation, Fed Chair Powell and other Federal Open Market Committee (FOMC) members have generally consistently maintained their hawkish rhetoric, even as inflation numbers have cooled down throughout the first three quarters of 2023. As of the end of the period, the market was a little more skeptical that the Fed will actually follow through on their hawkish comments. Regardless of whether the Fed is done hiking interest rates or if they end up further hiking rates, Barings believes that the market is in the last innings of this tightening rate cycle. Barings believes that the biggest question in the coming

13

fiscal year is whether the Fed can engineer a soft landing – or if the U.S. will slide into a recession. In Barings’ view, a recession would likely mean that the Fed would start easing rates sooner, whereas a soft landing could entail the Fed maintaining higher rates for a longer period of time. During this time, Barings plans to monitor Fed language carefully and act accordingly if they see signs of policy changing.

14

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

15

What is the investment approach of MassMutual Diversified Bond Fund, and who is the Fund’s subadviser?

The Fund seeks a superior total rate of return by investing in fixed income instruments. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in fixed income securities. The Fund’s subadviser is Barings LLC (Barings). In addition, Baring International Investment Limited serves as a sub-subadviser for the Fund.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 1.00%, outperforming the 0.64% return of the Bloomberg U.S. Aggregate Bond Index (the “benchmark”), which measures the performance of investment grade, U.S. dollar-denominated, fixed-rate taxable bond market securities, including Treasuries, government-related and corporate securities, mortgage-backed securities (MBS) (agency fixed-rate and hybrid ARM pass-throughs), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS). (“Agency” refers to debt issued by U.S. federal government agencies or government-sponsored entities for financing purposes.)

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, the Fund’s overweight allocation, relative to the benchmark, to investment-grade corporate credit contributed positively to performance, while the Fund’s overweight allocation to high-yield corporates also helped drive performance over the period. Allocations to other-finance, independent finance, and services/drilling were among the Fund’s top-performing industry positions over the period – while banks, brokers, cable, media, and technology were among the Fund’s top-detracting industry positions.

ABS, where the Fund held an overweight allocation, detracted from performance during the fiscal year. During a majority of the period, the asset class saw significant spread widening as a result of the market’s risk off tone amid the backdrop of increased rate volatility; however, the third quarter of 2023 showed a reversal of this trend. (Spreads represent the difference in yields between comparable Treasury and corporate bonds. Tightening spreads often reflect rising corporate bond prices; widening spreads often reflect falling corporate bond prices.) Over the third quarter of 2023, the ABS market remained mostly firm, with some sectors showing marginal tightening.

CMBS and residential mortgage-backed securities (RMBS) both detracted from relative performance over the period. The Fund’s underweight allocation to MBS contributed positively to returns. An allocation to high-quality short-weighted average life collateralized loan obligations (CLOs) contributed to performance during the period, as did the Fund’s underweight allocation to Treasuries.

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both. The Fund uses derivative instruments for yield curve, duration, downside hedging, and to gain exposures. They may also be used as a substitute as a direct investment. In aggregate, the Fund’s derivatives positions detracted from performance over the reporting period.

Subadviser outlook

In Barings’ observation, Fed Chair Powell and other Federal Open Market Committee (FOMC) members have generally consistently maintained their hawkish rhetoric, even as inflation numbers have cooled down throughout the first three quarters of 2023. As of the end of the period, the market was a little more skeptical that the Fed will actually follow through on their hawkish comments. Regardless of whether the Fed is done hiking interest rates or if they end up further hiking rates, Barings believes that the market is in the last innings of this tightening rate cycle. Barings believes that the biggest question in the coming fiscal year is whether the Fed can engineer a soft landing – or if the U.S. will slide into a recession. In Barings’ view, a recession would likely mean that the Fed would start easing rates sooner, whereas a soft landing could entail the Fed maintaining higher rates for a longer period of time. During this time, Barings plans to monitor Fed language carefully and act accordingly if they see signs of policy changing.

16

17

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

18

What is the investment approach of MassMutual High Yield Fund, and who is the Fund’s subadviser?

The Fund seeks to achieve a high level of total return, with an emphasis on current income, by investing primarily in high yield debt and related securities. The Fund invests primarily in lower rated U.S. debt securities (“junk” or “high yield” bonds), including securities in default. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in lower rated fixed income securities (rated below Baa3 by Moody’s, below BBB- by Standard & Poor’s or the equivalent by any nationally recognized statistical rating organization (using the lower rating) or, if unrated, determined to be of below investment grade quality by the Fund’s subadviser or sub-subadviser). The Fund’s subadviser is Barings LLC (Barings). In addition, Baring International Investment Limited serves as a sub-subadviser for the Fund.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Service Class shares returned 10.15%, underperforming the 10.28% return of the Bloomberg U.S. Corporate High-Yield Bond Index (the “benchmark”), which measures the performance of U.S. dollar-denominated, non-investment grade, fixed-rate, taxable corporate bonds, including corporate bonds, fixed-rate bullet, putable, and callable bonds, SEC Rule 144A securities, original issue zeros, pay-in-kind bonds, fixed-rate and fixed-to-floating capital securities.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the one-year period ended September 30, 2023, the U.S. bond market navigated rising interest rates, persistent inflation, and stress in the regional banking system to post strong double-digit returns. While higher-rated bonds outperformed into the end of 2022, risk appetite improved as 2023 began, as cyclicals and lower-rated securities drove the overall market.

Returns were positive across all industry sectors in which the Fund held positions during the period. Over the period, consumer cyclical led on increased probability of a soft economic landing, combined with strong risk appetite early in 2023, while energy posted above-market returns, despite moderation in energy prices from the prior year, as improved balance sheets and positive ratings momentum provided a tailwind. Communications continued to underperform as a result of declining advertising spend and elevated capital expenditures in the later cycle environment.

During the period, as it relates to the Fund, an underweight allocation to consumer cyclical was the primary detractor, whereas strong security selection within double-B and single-B bonds drove relative outperformance – and the Fund’s allocation across ratings categories was broadly neutral. Cash balances detracted, given the strong market return. The Fund’s strong security selection within capital goods, finance companies, and energy more than offset adverse selection within consumer non-cyclical and communications, while its overweight allocations to finance company, energy, and basic industry also positively contributed.

At the Fund holdings level, the largest detractors during the period were Radiology Partners, a hospital based, physician-owned radiology practice; Avaya, which provides solutions for internet protocol telephony, traditional voice communications, contact centers, and unified communications appliances; and Emergent BioSolutions, a specialty biopharmaceutical company. Conversely, the Fund’s top-performing credits during the period were Global Aircraft Leasing, an aircraft lessor; New Enterprise Stone and Lime, a construction materials supplier; and Nabors Industries, a global onshore oil and gas driller.

Subadviser outlook

Barings notes that, as hawkish Federal Open Market Committee (FOMC) rhetoric and solid macroeconomic data continued to contribute to push interest rates higher, investor expectations began to adjust toward a “higher for longer” rate environment as of the end of the fiscal period. Fund management’s macroeconomic forecasts project growth to slow modestly in the next year, although fundamental and technical factors could remain supportive. In Barings’ observation, high yield has historically performed well at the end of interest rate cycles and periods of slower economic growth, particularly in comparison to equity markets. In Barings’ experience, income within the asset class generally provides a cushion against volatility, especially when considering sizable discounts to par and elevated yields already priced into the market.

19

20

GROWTH OF $10,000 INVESTMENT - Service Class

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

21

What is the investment approach of MassMutual Balanced Fund, and who is the Fund’s subadviser?

The Fund seeks a high total return by investing across different asset classes (U.S. equity securities and fixed income securities) each represented by a different segment of the Fund’s portfolio. Under normal market conditions, the Fund’s subadviser and sub-subadviser expect that 55%-75% of the Fund’s net assets will be invested in U.S. equity securities (the “U.S. Equity Segment”) and 25%-45% of the Fund’s net assets will be invested in fixed income securities (the “Bond Segment”) that meet certain environmental, social, and governance (“ESG”) criteria. The Fund will target a long term strategic allocation of 65% to the U.S. Equity Segment and 35% to the Bond Segment. The Fund’s subadviser is Invesco Advisers, Inc., and its sub-subadviser is Invesco Capital Management LLC (together with Invesco Advisers, Inc., “Invesco”).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 10.76%, underperforming, by a wide margin, the 21.62% return of the S&P 500^® Index (the “stock component’s benchmark”), which measures the performance of 500 widely held stocks in the U.S. equity market. The Fund’s Class R5 shares outperformed, by a wide margin, the 0.64% return of the Bloomberg U.S. Aggregate Bond Index (the “bond component’s benchmark”), which measures the performance of investment grade, U.S. dollar-denominated, fixed-rate taxable bond market securities, including Treasuries, government-related and corporate securities, mortgage-backed securities (MBS) (agency fixed-rate and hybrid ARM pass-throughs), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS). (“Agency” refers to debt issued by U.S. federal government agencies or government-sponsored entities for financing purposes.) Additionally, the Fund’s Class R5 shares underperformed the 11.23% return of the Lipper Balanced Fund Index, an unmanaged, equally weighted index of the 30 largest mutual funds within the Lipper Balanced Category; and underperformed the 14.07% return of the Custom Balanced Index, which comprises the stock component’s benchmark and the bond component’s benchmark. The weightings of each index in the Custom Balanced Index are 65% and 35%, respectively.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s stock component performance

The Fund’s equity component (what Invesco refers to as the “equity sleeve”) is passively managed and seeks to closely track the investment results, before fees and expenses, of the Invesco US Large Cap Total Balanced Multi-Factor ESG Index (the “Index”). The Index employs a security-ranking model applied to U.S. large-capitalization equities with best-in-class Environmental, Social, and Governance (ESG) scores, while excluding certain industries (e.g., tobacco, aerospace, coal, and pipelines) and controversial companies. The model is based on four well-established factors, which are equally weighted: quality, value, price momentum, and low volatility.

Over the reporting period, the equity sleeve underperformed the stock component’s benchmark. With equity volatility declining sharply over the first half of 2023 and remaining significantly beneath its 2022 and long-term average levels, low volatility as the high-performing factor over the prior year was challenged early in 2023. Riskier large-cap names broadly outperformed over the first and second quarters of 2023, with the more cyclically oriented industries, such as automobiles and online services, benefiting in particular from the change in risk preferences.

Over the reporting period, low volatility and price momentum factors were the primary detractors from performance relative to the stock component’s benchmark. Quality factors made a positive contribution to results over the period, while value factors had mixed results and generally had a minimal overall impact on relative performance for the equity sleeve.

Subadviser discussion of factors that contributed to the Fund’s bond component performance

The performance of the Fund’s fixed income component (what Invesco refers to as the “fixed income sleeve”) slightly trailed the bond component’s benchmark for the reporting period, with curve positioning serving as the leading detractor, given the continued rise in interest rates across the curve. (The yield curve is a graph showing the term structure of interest rates by plotting the yields of all bonds of comparable quality with maturities ranging from the shortest – typically one month – to the longest – typically 30 years – available. The resulting curve shows whether short-term interest rates are higher or lower than long-term rates.) During the period, front-end Treasury exposure was the primary headwind for the fixed income sleeve, as Federal Reserve

22

policy continued to drive yields higher, while longer-duration credit proved additive. Duration is a measure of a bond fund’s sensitivity to interest rates. The longer the duration, the greater the price impact on the bond or portfolio when interest rates rise or fall. Within the fixed income sleeve’s credit allocation, holdings in the industrial sector contributed during the period, given overweight allocations (relative to the benchmark) to and favorable security selections within the communications, energy, and technology sub-sectors, while underweight allocations to capital goods and basic industries were headwinds. The financial sector was a detractor, led primarily by weaker performance in the regional banking sub-sector during the period. Down-in-quality investment-grade issues outperformed higher-quality bonds, which yielded a favorable result, given the fixed income sleeve’s overweight allocation to BBBs; however, security selection served as a negative offset. Within structured credit, the slightly overweight allocation to MBS was a modest detractor, as interest rate volatility weighed on the sector during the sector, while security selections in ABS and CMBS positively contributed.

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both. The Fund’s use of futures had a net positive effect on performance during the reporting period.

Subadviser outlook

Looking ahead, Invesco expects a “bumpy landing” – a relatively brief and shallow economic slowdown driven by aggressive monetary policy tightening. Fund management continues to believe that the U.S. could avoid a substantial broad-based recession because of its tight labor market. Invesco expects markets to start to discount a more positive environment for economic growth later in 2024. As of the end of the period, Fund management believes the U.S. is at a policy peak and the market is experiencing disinflation alongside a relatively brief global economic slowdown. However, Fund management expect markets to ultimately look past this episode and begin to discount a future economic recovery. In this environment, Invesco anticipates near-term outperformance of somewhat defensive asset classes, such as high-quality corporate bonds, as well as growth and quality larger-cap equities, especially technology, consumer products, and services. They also expect markets to discount an economic recovery in developed economies, which Invesco believes could lead to the potential outperformance of more “risk-on” asset classes, such as high-yield credit and cyclical and smaller-cap non-U.S. equities.

23

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

24

What is the investment approach of MassMutual Disciplined Value Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return by investing primarily in equity securities of U.S. large- and mid-cap companies. The Fund currently invests substantially all of its assets in companies represented in the Russell 1000^® Value Index at the time of purchase, although the Fund is actively managed and is not an index fund or a passively managed investment. Constituents of the Russell 1000 Value Index are companies that exhibit certain value characteristics, as defined by the index providers, such as lower price-to-book ratios, lower prices relative to forecasted earnings, and higher dividend yields. The Fund’s subadviser is Wellington Management Company LLP (Wellington Management).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Service Class shares returned 14.95%, outperforming the 14.44% return of the Russell 1000 Value Index (the “benchmark”), which measures the performance of the large-cap value segment of U.S. equity securities. It includes the Russell 1000 Index companies with lower price-to-book ratios and lower expected growth values. It is market-capitalization weighted.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, strong security selection and positive sector allocation were the primary drivers of the Fund’s outperformance.

The impact of security selection, which is a byproduct of the Fund’s systematic factor construction process, was positive for the period, led by strong selection in the financial, utilities, and information technology sectors. This was only partially offset by less-than-favorable stock selection in the industrial, health care, and real estate sectors.

Sector allocation is a fallout of the Fund’s factor implementation process and factors will rotate in and out of sectors over time. During the period, the Fund’s sector allocation contributed to relative performance, led by an underweight allocation to the utilities sector and an overweight exposure to the information technology sector. This was partially offset by the Fund’s underweight exposures to the communication services and energy sectors, which detracted from relative results.

The Fund’s overweight position in Meta Platforms (communication services), the parent company of Facebook and Instagram, and Fund management’s decision to not own American energy company NextEra Energy (utilities) were the two largest contributors to relative results during the period. Fund management eliminated the Fund’s position in Meta Platforms during the period. The Fund’s overweight positions in weaker-performing stocks including real estate investment trust SBA Communications (real estate) and American telecommunications company Lumen Technologies (communication services) were the two largest relative detractors during the period. Fund management increased the Fund’s overweight exposure to SBA Communications and eliminated the Fund’s stake in Lumen Technologies as of the end of the reporting period.

Subadviser outlook

Wellington Management expects volatility to persist as macroeconomic themes develop and investors react to the potential for persistently higher interest rates, elevated inflation, and volatile energy prices. Fund management is cognizant of pockets of the value universe that face a heightened risk of insolvency as of the end of the period, as well as the volatile impact that macro risks can have on deeper value names. When constructing the Fund’s portfolio, Fund management generally leans into a diversified, discounted cash flow-based value factor that identifies opportunities by focusing on a company’s future cash flow pattern, which their research shows can be more insulated from these risks. In screening for value names with strong fundamental momentum, Fund management typically looks for companies where earnings translate to cash flows and where earnings estimates are rising. In Wellington Management’s experience, this often leads to Fund holdings that are lower-duration growth stocks and helps the Fund avoid many speculative names that are sensitive to a higher interest rate regime. Finally, Fund management typically endeavors to maintain exposure to defensive stocks in the value universe by investing in companies with more stable economic profits, which can help the portfolio weather the storm of a potential market downturn.

25

26

GROWTH OF $10,000 INVESTMENT - Service Class

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

27

What is the investment approach of MassMutual Main Street Fund, and who is the Fund’s subadviser?

The Fund seeks a high total return by investing primarily in common stocks of U.S. companies of different capitalization ranges. The Fund’s subadviser currently focuses on “large capitalization” issuers, which are considered to be companies with market capitalizations at the time of purchase within the market capitalization range of companies included within the Russell 1000^® Index, although it may purchase stocks of companies with any market capitalization. The Fund’s subadviser is Invesco Advisers, Inc. (Invesco Advisers).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 19.37%, underperforming the 21.62% return of the S&P 500^® Index (the “benchmark”), which measures the performance of 500 widely held stocks in the U.S. equity market.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, stock selection in the information technology and industrial sectors and an overweight allocation, relative to the benchmark, to the financial sector were the primary drivers of the Fund’s underperformance. This was partially offset by stronger stock selection in the communication services, health care, and real estate sectors.

With respect to specific Fund holdings during the period, the top contributors to the Fund’s relative performance included Meta, Netflix, and Applied Materials. American multinational technology corporation Meta outperformed during the reporting period as the company returned to revenue growth and continued to benefit from the meaningful steps taken to optimize its cost structure and improve execution. American content platform and production company Netflix experienced improved subscriber growth and had early success with new revenue growth opportunities during the period, including the launch of an ad-based tier and a crackdown on password sharing. Applied Materials, a semiconductor equipment company, performed well during the period along with the technology sector as a whole and higher-growth stocks in general. The company also benefited from a normalization of the supply chain that had been disrupted during the pandemic.

On the downside, Fund holdings that were top detractors from relative performance during the period included Charles Schwab, Dominion Energy, and United Parcel Services. Not owning Nvidia for a portion of the period was another key detractor from relative returns, given the stock’s significant gains. Charles Schwab was negatively impacted by the banking crises that began with the failure of Silicon Valley Bank (not a Fund holding). Like many financial institutions, Charles Schwab was heavily scrutinized in the market during the period for unrealized losses in their securities portfolio.

Dominion underperformed, along with the utilities sector, given the rising interest rate environment during the reporting period, which has historically been a headwind to utilities. The company sold some assets to reduce its leverage, but there was uncertainty with the process and the likely proceeds. There was also legislation in Virginia that mandated a reduction in Dominion’s customer bills. United Parcel Services was negatively impacted by a deceleration in U.S. retail sales and ongoing challenges in Asia during the period. Additionally, the potential for a labor strike disruption added to negative sentiment during the reporting period.

Subadviser outlook

Invesco Advisers notes that as of the end of the period, key inflation measures remained well above the Federal Reserve’s (the “Fed”) target, and rising fuel prices caused inflation to re-accelerate late in the third quarter of 2023. The Fed repeated its pattern from the second quarter of 2023, as it hiked its target federal funds rate (the Fed’s overnight bank lending rate) in July and then paused in September, while telegraphing to the markets that interest rates were likely to remain high for an extended period of time in an effort to combat stubbornly high inflation. While gross domestic product (GDP) growth remains positive, economic risks have increased in Invesco Advisers’ view. As of the end of the period, those risks included numerous labor strikes and the threat of a federal government shutdown that threaten to drag down the economy.

28

Invesco Advisers observes that a more challenging market sentiment does not change their approach to investing, which generally favors better-managed companies with strong balance sheets and competitive positioning. In Fund management’s view, such companies should be relatively less dependent on higher-cost debt financing and be able to better defend profit margins.

29

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

30

What is the investment approach of MassMutual Disciplined Growth Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return by investing primarily in equity securities of U.S. large- and mid-cap companies. The Fund currently invests substantially all of its assets in companies represented in the Russell 1000^® Growth Index at the time of purchase, although the Fund is actively managed and is not an index fund or a passively managed investment. Constituents of the Russell 1000 Growth Index are companies that exhibit certain growth characteristics, as defined by the index providers, such as historical and predicted future earnings per share growth rates and trends, historical sales per share growth trends, and internal growth rate. The Fund’s subadviser is Wellington Management Company LLP (Wellington Management).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Service Class shares returned 23.44%, underperforming the 27.72% return of the Russell 1000 Growth Index (the “benchmark”), which measures the performance of the large-cap growth segment of U.S. equity securities. It includes the Russell 1000 Index companies with higher price-to-book ratios and higher forecasted growth values. It is market-capitalization weighted.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, security selection drove the Fund’s underperformance, while sector allocation contributed. The impact of security selection was the primary driver of underperformance during the reporting period, led by weak selection in the information technology, health care, industrial, and materials sectors. This was only partially offset by stronger stock choices in the communication services sector.

Sector allocation is a fallout of Wellington Management’s factor implementation process, and factors will rotate in and out of sectors over time. During the period, sector allocation contributed to performance, led by the Fund’s overweight exposure, relative to the benchmark, to the information technology sector and its underweight allocations to the health care and real estate sectors. This was partially offset by the Fund’s overweight allocation to the financial sector, which detracted from relative results.

The Fund’s underweight position in American multinational technology company Nvidia (information technology) and its overweight allocation to American specialty chemicals manufacturing company Albemarle (materials) were the two largest detractors from relative results during the period. Fund management increased the Fund’s exposure to Nvidia, taking the Fund to an overweight position as of the end of the reporting period. Fund management eliminated its position in Albemarle during the fiscal year. The Fund’s overweight exposures to Meta Platforms (communication services), the parent company of Facebook and Instagram, and American semiconductor company Broadcom (information technology) were the two largest contributors to relative results during the period.

Subadviser outlook

Wellington Management notes that, despite significant positive returns early in the year, growth stocks face persistent macro uncertainties, and some investors may be contemplating if the run-up in growth is sustainable. Notably, Fund management is watching the potential ramifications of interest rates that could stay higher for longer, elevated inflation, and the outsized impact of a select few stocks on the broader U.S. market.

Wellington Management remains committed to managing related risks and factor exposures across the Fund’s portfolio. In their exposure to growth stocks with attractive valuations, Fund management remains cautious of structural risks that may be embedded in a company’s share price (e.g., high levels of corporate leverage or illiquidity). In screening for growth names with strong fundamental momentum, Fund management typically looks for companies where earnings translate to cash flows and where earnings estimates are rising. This generally leads Wellington Management to own lower-duration growth stocks and avoid many speculative names that are sensitive to a higher interest rate regime. Finally, Fund management endeavors to balance these positions with exposure to the highest-quality companies in the growth universe: those with high and stable returns on capital and strong balance sheets.

31

32

GROWTH OF $10,000 INVESTMENT - Service Class

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

33

What is the investment approach of MassMutual Small Cap Opportunities Fund, and who is the Fund’s subadviser?

The Fund seeks capital appreciation by investing primarily in common stocks of small-capitalization U.S. companies that the Fund’s subadviser believes have favorable business trends or prospects based on fundamental analysis. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in securities of small-cap companies. The Fund’s subadviser is Invesco Advisers, Inc. (Invesco Advisers).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class A shares returned 12.53%, outperforming the 8.93% return of the Russell 2000^® Index (the “benchmark”), which measures the performance of the small-cap segment of the U.S. equity universe. It is a subset of the Russell 3000 Index and includes approximately 2000 of the smallest securities based on a combination of their market cap and current index membership.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, stock selection in the health care, consumer staples, and consumer discretionary sectors was the primary driver of the Fund’s outperformance. This was partially offset by weaker stock selection in the information technology, financial, and energy sectors.

Fund holdings that were the top contributors to the Fund’s relative performance during the period included Reata Pharmaceuticals, Atkore, and BellRing Brands. Reata, a biopharmaceutical company focused on novel therapeutics for patients with serious or life-threatening diseases, was acquired for a significant premium by Biogen (not a Fund holding) during the period. Atkore, a manufacturer of electrical products, was a beneficiary of an inflationary environment, as it drove strong pricing for many of its key building products. BellRing continued to gain market share in its core nutrition products, including shakes and nutrition bars. Furthermore, the company benefited from improvements in its supply chain during the period, which had been limiting its ability to expand production and expand volume growth.

On the downside, Fund holdings that were top detractors from relative performance during the period included Paycor, Columbia Banking System, and Acadia Healthcare. Paycor, a provider of human capital management solutions through a software-as-a-service platform, underperformed, as valuation multiples for higher-growth software companies came under pressure due to macro concerns, including inflation and a rising rate environment, which could potentially result in a weaker demand backdrop. Columbia Banking System’s stock price came under pressure, along with regional banks in general, after the failure of two other regional U.S. banks in February 2023 negatively impacted investor sentiment toward the entire group. Acadia, a provider of behavioral health care services, was negatively impacted by wage inflation that increased the company’s expenses.

Subadviser outlook

Invesco Advisers notes that as of the end of the period, key inflation measures remained well above the Federal Reserve’s (the “Fed”) target, and rising fuel prices caused inflation to re-accelerate late in the third quarter of 2023. The Fed repeated its pattern from the second quarter of 2023, as it hiked its target federal funds rate (the Fed’s overnight bank lending rate) in July and then paused in September, while telegraphing to the markets that interest rates were likely to remain high for an extended period of time in an effort to combat stubbornly high inflation. While gross domestic product (GDP) growth remains positive, economic risks have increased in Invesco Advisers’ view. As of the end of the period, those risks included numerous labor strikes and the threat of a federal government shutdown that threaten to drag down the economy.

34

35

GROWTH OF $10,000 INVESTMENT - Class A

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

36

What is the investment approach of MassMutual Global Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital appreciation by investing primarily in common stocks of companies in the U.S. and foreign countries. The Fund can invest without limit in foreign securities, including American Depositary Receipts (ADRs), and can invest in any country, including developing or emerging market countries. However, the Fund currently emphasizes investments in developed markets such as the United States, Western European countries, and Japan. As a fundamental policy, the Fund normally will invest in at least three countries (one of which may be the United States). Typically, the Fund invests in a number of different countries. The Fund’s subadviser is Invesco Advisers, Inc. (Invesco Advisers).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 28.99%, outperforming, by a wide margin, the 20.80% return of the MSCI All Country World Index (ACWI) (the “benchmark”), which measures the performance of the large- and mid-cap segments of all country markets. It is free float-adjusted market-capitalization weighted.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, the Fund outperformed the benchmark in nine of 11 Global Industry Classification Standard (GICS) sectors. Stock selection in communication services, health care, and real estate added the most to relative performance. On the other hand, stock selection in consumer discretionary and an underweight allocation to the energy sector detracted from relative returns.

From a regional perspective, stock selection in the United States and Denmark, along with the Fund’s overweight allocation to France, added the most to relative performance. Conversely, stock selection in China, Japan, and Switzerland detracted most from the Fund’s results.

With respect to specific Fund holdings during the period, the top two individual contributors were Meta Platforms, the parent company of Facebook and Instagram, and Alphabet, the parent company of Google. Meta Platforms (United States) improved its performance in the first three quarters of 2023 after a difficult 2022. The company maintained its strong network effect advantage, with its user base growing across all applications, engagement remaining resilient, and further monetization improvements being seen during the second quarter of 2023. As of the end of the period, advertisers were more confident in Meta’s artificial intelligence-powered ad capabilities. During the period, Meta also implemented overall cost-cutting and efficiency improvements. In Fund management’s view, Alphabet (United States) is one of the best-positioned companies with respect to innovation. In the first three quarters of 2023, the company experienced positive indicators including: stabilized advertising demand, accelerated Search and YouTube growth, resilient Cloud growth and yields from the company’s focus on efficiency.

On the downside, the Fund’s top two individual detractors during the period were JD.com and Meituan. JD.com (China) is a major player in Chinese e-commerce, offering a wide selection of authentic products at competitive prices, with fast and reliable delivery. The shares trended lower over the course of the fiscal year, as the Chinese Covid lockdowns weighed on economic growth, and the subsequent recovery was underwhelming. Like many other Chinese stocks, JD.com’s results in the first half of 2023, as well as its outlook, were quite muted. The company’s second-quarter results were disappointing, with zero year-on-year growth in operating profit from its main segment, JD Retail, underperforming its peers. Meituan (China) is the largest food delivery service in China. The company struggled over the past fiscal year due to weak economic growth in China and increased competition.

Subadviser outlook

Invesco Advisers notes that, as the market continues to move into a regime in which capital has an appreciable cost, they believe that quality characteristics will continue to play a pivotal role in market outcomes. Generally, the high-quality companies the Fund owns have, in Fund management’s view, strong balance sheets, excellent management teams, sustainable competitive advantages, and robust operating cash flow. In Fund management’s view, these characteristics become even more crucial as

37

liquidity conditions become challenging and the cost of capital rises. Notably, strong operating cash flow generally provides companies with a solid financial foundation, contributing to their ability to withstand market volatility, maintain business continuity, and navigate periods of reduced liquidity. Looking into the future, Fund management strongly believes that investment themes like the cloud, automation, medical diagnostics, the electrification of everything, high-end luxury, and travel, among others, have the potential to continue to contribute to or lead the global economy.

38

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

39

What is the investment approach of MassMutual International Equity Fund, and who are the Fund’s subadvisers?

The Fund seeks to achieve long-term capital appreciation by investing primarily in common stock of foreign companies. The Fund invests primarily in the common stock of companies that are domiciled or that have their primary operations outside of the United States. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in securities of foreign companies. The Fund may invest up to 100% of its total assets in such securities. The Fund may invest in emerging markets as well as in developed markets throughout the world. From time to time, the Fund may place greater emphasis on investing in one or more particular regions (such as Asia, Europe, or Latin America). The Fund’s subadvisers are Wellington Management Company LLP (Wellington Management), which managed approximately 74% of the Fund’s portfolio; and Thompson, Siegel & Walmsley LLC (TSW), which was responsible for approximately 26% of the Fund’s portfolio, as of September 30, 2023.

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 17.48%, underperforming the 20.39% return of the MSCI All Country World Index (ACWI) ex USA (the “benchmark”), which measures the performance of the large- and mid-cap segments of the particular regions, excluding U.S. equity securities, including developed and emerging markets. It is free float-adjusted market-capitalization weighted.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

Within the Wellington Management Fund component, weak stock selection drove relative results during the period, particularly within the financial, consumer staples, and industrial sectors. This was partially offset by strong selection within consumer discretionary, materials, and energy. Sector allocation also detracted from relative performance. Overweight allocations to consumer staples and health care and an underweight to the financial sector detracted most. This was partially offset by a lack of exposure to real estate and an overweight allocation to the industrial sector. With respect to specific Fund component holdings, top detractors from relative performance included Diageo (consumer staples) and an out-of-benchmark position in Canadian National Railway (industrials). Shares of Diageo fell during the period despite the U.K.-based global spirits company releasing strong fiscal 2023 full-year results. While growth was strong across most regions, sales of spirits in North America stalled as the U.S. dealt with inflationary pressures during the period. Shares of Canadian National Railway lagged due to market fears of an economic slowdown, as well as continued destocking in North American retail inventory, which pressured volumes in their intermodal business during the period. Fund component holdings that were top contributors to relative returns during the period included Industria de Diseño (consumer discretionary) and BAE Systems (industrials). Shares of Spanish clothing retailer Industria de Diseño gained, as the company posted stronger-than-expected results due to the generally unexpectedly resilient European consumer. The share price of BAE Systems rose during the period; the international defense, aerospace, and security company experienced accelerating organic growth due to key program wins and an acquisition announcement.

For the one-year period ended September 30, 2023, within the TSW component of the Fund, stock selection within Japan detracted most from relative returns. The top detractor from the Fund component’s performance in this regard was Fund component holding Seven & I, a Japanese diversified retail holding company known in the U.S. for their 7-11 franchise. Seven & I investors were disappointed that a slate of independent board candidates put forth by an activist group did not win seats in the second quarter of 2023. From a traditional attribution lens, stock selection within Europe contributed most to relative results during the period. Stock selection was on display during the period, as contributions came from an array of Fund component holdings from various industries. The top contributor to the Fund component’s performance in this regard was AIB Group plc, which benefited from a relatively strong local economy and a rising interest rate environment during the period. From a sector perspective, the Fund component’s underweight allocation, relative to benchmark, to the consumer discretionary sector - one of the market’s top-performing sectors during the period - weighed the most on relative returns due to a combination of unfavorable positioning and stock selection This was particularly evident with respect to TSW’s light exposure to pro-cyclical industry groups, such as luxury goods and hotels. Fund component holding Rakuten, an e-commerce giant, dragged on results, as the company continued to invest heavily in the rollout of its mobile telecommunications offering (which had yet to turn profitable

40

as of the end of the period). The industrial sector contributed most to relative return, thanks to a combination of positive stock selection and overweight exposure to one of the leading market sectors. Numerous Fund component holdings from varying industrial sector groups enjoyed better-than-market returns. A top contributor in this regard was Fund component holding Toyota Industries, a Japanese holding company which serves as a leading manufacturer of forklifts and has a stake in Toyota Motor Company. During the period, Toyota Industries benefited from the outperformance of Japanese equities – specifically, their stake in Toyota Motor, which is a significant Japanese index constituent.

Subadviser outlook

Wellington Management notes that its Fund component owns high-quality companies that have the potential to compound their value over time and be resilient to downside risk. Fund management believes that the current rising interest rate environment could have an impact on growth and that signs of slowing could emerge within the next few quarters. China continues to be slow after an underwhelming post-COVID reopening and the outlook for Europe is not strong. Fund management feels there are clouds on the horizon, but that their Fund component’s portfolio is well positioned to weather the storm.

TSW observed that stubborn interest rates overwhelmed surprisingly resilient economic indicators during the period, sending global equity markets downward in the third quarter of 2023. Investor confidence in the near-term outlook is shaky, in Fund management’s view – a sentiment that Fund management believes is reinforced by cautious guidance statements from companies across many industries and regions. In TSW’s view, although many stocks may look relatively inexpensive, the valuation alone may be sufficient to bring investors off the sidelines in the short term. TSW believes conditions like this are beneficial to investors with a longer investment horizon and the patience to ride through the market disturbance and economic adjustments that accompany a “higher-for-longer” interest rate regime.

41

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

42

What is the investment approach of MassMutual Strategic Emerging Markets Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital growth by investing mainly in common stocks of issuers in developing and emerging markets throughout the world and at times may invest up to 100% of its total assets in foreign securities. Under normal market conditions, the Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of issuers whose principal activities are in a developing (or emerging) market, i.e., are in a developing market or are economically tied to a developing market country. The Fund will invest in at least three developing markets. In general, countries may be considered developing or emerging markets if they are included in any one of the MSCI emerging markets indexes, classified as a developing or emerging market, or classified under a similar or corresponding classification, by organizations such as the World Bank and the International Monetary Fund, or have economies, industries, and stock markets with similar characteristics. The Fund’s subadviser is Invesco Advisers, Inc. (Invesco Advisers).

How did the Fund perform during the 12 months ended September 30, 2023?

The Fund’s Class R5 shares returned 14.37%, outperforming the 11.70% return of the MSCI Emerging Markets Index (the “benchmark”), which measures the performance of the large- and mid-cap segments of emerging market equity securities. It is free float-adjusted market-capitalization weighted.

For a discussion on the economic and market environment during the 12-month period ended September 30, 2023, please see the Economic and Market Overview, beginning on page 1.

Subadviser discussion of factors that contributed to the Fund’s performance

For the fiscal year ended September 30, 2023, the Fund delivered strong absolute performance and outperformed the benchmark. The key contributors to performance included stock selection within the materials, energy, and consumer discretionary sectors.

The Fund was able to realize value from Russian investments, which contributed to performance alongside stock selection in China and an overweight allocation, relative to the benchmark, to Mexico. Grupo Mexico – a diversified mining company and a world leader in copper production – was among the largest absolute and relative contributors to performance during the period. As of the end of the period, this Fund holding had the largest proven copper reserves in the world, which contributed to investor confidence in future production levels and efficiencies. Additionally, Housing Development Finance Corporation (HDFC) – the first specialized mortgage company in India – was a notable contributor to absolute performance. During the period, HDFC merged with its subsidiary, HDFC Bank, which contributed to investor confidence in the combined entity’s efficiencies and advantages, particularly as mortgage penetration and consumer finance remained embryonic in India. Taiwan Semiconductor Manufacturing Company, one of the world’s leading semiconductor foundries, was also a significant contributor to absolute performance. As of the end of the period, the company was a key contributor to the computing revolution, with multiple architectures, chip platforms, and design teams competing to advance progress in computing and artificial intelligence (AI) innovation.

Stock selection and an underweight allocation in the information technology sector, along with stock selection in the financials and consumer staples sectors, detracted most from relative performance during the reporting period. Stock selection and an underweight allocation in South Korea detracted most on a country level from relative performance. Additionally, an overweight allocation in India and stock selection in Brazil detracted from performance. Meituan – which operates a leading service-based e-commerce platform in China, facilitating food delivery and restaurant reservations, among other services – was the largest absolute detractor from performance. The company’s share price contracted during the period amid a challenging macro environment and competitive backdrop in China.

Subadviser outlook

Invesco Advisers sees substantial polarization of markets today, with perceived macroeconomic “certainty” being priced exceptionally tightly and valuations looking exceptionally attractive in areas of uncertainty. As experienced emerging-market investors recognize, extreme periods may present opportunity for the patient investor. As of the end of the period, emerging-market equity valuations looked attractive on a relative basis, and Fund management sees a few catalysts that it believes could crystalize that value.

43

Invesco Advisers remains a long-term investor, and generally does not make tactical decisions. Invesco Advisers believes that unfavorable industry trends have historically created opportunities for truly skilled active managers. Fund management believes the current environment favors those with an idiosyncratic approach and rewards genuine imagination and creativity in unearthing the rare breed of extraordinary companies. Invesco Advisers believes that company fundamentals are especially crucial to long-term emerging-market investors. Invesco Advisers’ investment approach has always been rooted in the unwavering focus on high-quality compounders. Fund management believes long-term investors are well-served by gaining exposure to truly innovative emerging-market companies capitalizing on structural tailwinds.

44

GROWTH OF $10,000 INVESTMENT - Class R5

The graph above illustrates a representative class of the Fund’s historical performance for the past 10 fiscal years or since inception (for Funds lacking 10-year records) in comparison to its benchmark index, as well as one or more additional indexes, if applicable. The performance of other share classes will be greater than or less than the class depicted above.

Generally accepted accounting principles require adjustments to be made to the net assets of the Fund at period end for financial reporting purposes only, and as such, the total return based on the unadjusted net asset value per share may differ from the total return reported in the financial highlights.

Performance results in the graph and table are shown both with and without the imposition of the maximum applicable sales charge (if applicable) and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. Investors should note that the Fund is a professionally managed mutual fund, while the index or indexes shown above are unmanaged, cannot be purchased directly, and, with the exception of any peer group index, do not incur expenses.

Performance data quoted in the graph and table represents past performance; past performance is not predictive of future results. The investment return and principal value of shares of the Fund fluctuate, so your shares, when sold, may be worth more or less than their original cost. Current performance of the Fund may be lower or higher than the performance quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on Fund distributions or the redemption of Fund shares. Performance data current to the most recent month end may be obtained by calling 1-888-309-3539.

Investors should read the Fund’s prospectus with regard to the Fund’s investment objectives, risks, and charges and expenses in conjunction with these financial statements. Employee retirement benefit plans that invest plan assets in the Separate Investment Accounts (SIAs) may be subject to certain charges as set forth in their respective Plan Documents. Total return figures would be lower for the periods presented if they reflected these charges.

45

Abbreviation Legend

Notes to Portfolio of Investments

Percentages are stated as a percent of net assets.

The accompanying notes are an integral part of the financial statements.

46

The accompanying notes are an integral part of the financial statements.

47