MML Series Investment Fund 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 MML Series Investment Fund. 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.

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To Our Shareholders

Paul LaPiana

“We recognize that talking about your future can be uncomfortable. That’s why we’re here – to support you throughout your retirement planning journey. For nearly 170 years, through ups and downs and good times and bad, MassMutual has helped its clients protect their loved ones and prepare for a better tomorrow.”

December 31, 2021

The return of market volatility and inflation challenges retirement investors

I am pleased to present you with the MML Series Investment Fund Annual Report. For the reporting period from January 1, 2021 through December 31, 2021, U.S. stocks were up nearly 29%, with investors moving past the global economic recession and market downturn brought on by the COVID-19 pandemic. Foreign stocks in developed markets also experienced strong gains during the year, aided by increasing economic activity, generous fiscal and monetary stimulus, and strong corporate earnings throughout the reporting period. Emerging-market stocks ended the year down, led by Chinese stocks that faced unexpected regulatory action and debt defaults in the Chinese real estate sector. U.S. bond investors experienced negative returns in the rising interest rate environment, fueled by an increase in economic growth expectations, heighted inflationary pressures, and a lessening of monetary and fiscal policy support.

Suggestions for retirement investors under any market conditions

Is it time to track your progress?

If you work with a financial professional, you may wish to consider checking in with him or her to help you determine if:

* Systematic investing and asset allocation do not ensure a profit or protect against loss in a declining market. Systematic investing involves continuous investment in securities regardless of fluctuating price levels. Investors should consider their ability to continue investing through periods of low price levels.

(Continued)

1

We’re here to help you build the future you want for yourself and your family.

We recognize that talking about your future can be uncomfortable. That’s why we’re here – to support you throughout your retirement planning journey. For nearly 170 years, through ups and downs and good times and bad, MassMutual has helped its clients protect their loved ones and prepare for a better tomorrow. So we continue to encourage you to maintain perspective when it comes to retirement investing, regardless of any short-term changes in the markets or headline-making events that may be unsettling. Our view is that changing market conditions have the potential to reward patient investors.

Sincerely,

Paul LaPiana
President
MML Series Investment Fund
MML Investment Advisers, LLC

^© 2022 Massachusetts Mutual Life Insurance Company (MassMutual^®), Springfield, MA 01111-0001. All rights reserved www.MassMutual.com. Underwriter: MML Distributors, LLC. (MMLD) Member FINRA and SIPC (www.FINRA.org and www.SIPC.org), 1295 State Street, Springfield, MA 01111-0001. MMLD is a wholly-owned subsidiary of MassMutual. Investment advisory services provided to the Funds by MML Investment Advisers, LLC (MML Advisers), a wholly-owned subsidiary of MassMutual.

The information provided is the opinion of 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.

RS-50733-00

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December 31, 2021

Market Highlights

Market Environment

Global stock investors experienced declining levels of volatility and strong positive returns for the year beginning January 1, 2021. U.S. stocks rose steadily in the period, buoyed by the Fed’s commitment to low interest rates, additional rounds of fiscal stimulus, rising expectations for strong economic growth, and rebounding corporate earnings. As a result, the broad market S&P 500^® Index* (the “S&P 500”) delivered a strong 28.71% return for the year. The Dow Jones Industrial Average^SM was also up a respectable 20.95%. The technology-heavy NASDAQ Composite Index was also a big winner, advancing 22.18% for the year. Small-cap stocks underperformed their larger peers, as small-caps gained 14.82% – while value stocks and their growth counterparts performed similarly.

The continued market recovery, additional fiscal stimulus, conclusion of the U.S. presidential election, expectations for the tightening of monetary policy, and heightened inflationary pressures affected sectors differently, though all 11 sectors were in positive territory for the year. The energy, real estate, and financial sectors led in performance, enjoying double-digit growth, as they outperformed the S&P 500.

The energy sector was the strongest performer for the year, up over 54%, aided by a 55% increase in the price of West Texas Intermediate crude oil during the period. The utilities and consumer staples sectors trailed the S&P 500, each by more than 10%.

* Indexes referenced, other than the MSCI Indexes, are unmanaged, do not incur fees, expenses, or taxes, and cannot be purchased directly for investment. The MSCI Indexes are unmanaged, do not incur fees or expenses, and cannot be purchased directly for investment.

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Developed international markets, as measured by the MSCI EAFE^® Index, trailed their domestic peers, ending the year up 11.26%. Developed international stocks benefited from increasing economic activity, generous fiscal and monetary stimulus, and strong corporate earnings during the year. Emerging-market stocks, as measured by the MSCI Emerging Markets Index, ended down 2.54% for the period, led by Chinese stocks that faced unexpected regulatory action and debt defaults in the Chinese real estate sector.

Bond yields rose sharply during the year, with the 10-year U.S. Treasury bond yield rising from a low of 0.93% on January 4, 2021 to close the period at 1.52%. Rising yields generally produce falling bond prices; consequently, bond index returns suffered. The Bloomberg U.S. Aggregate Bond Index ended the period down 1.54%. Investment-grade corporate bonds fared somewhat better. The Bloomberg U.S. Corporate Bond Index, which tracks investment-grade corporate bonds, ended the period down only 1.04%. The Bloomberg U.S. Corporate High Yield Bond Index ended in positive territory, advancing 5.28%, aided by a sharp increase in commodity prices.

As we enter 2022, we view the stock markets as extended and valuations high relative to market history. While the prospect of lower financing costs, strong economic and corporate earnings growth, and continued government commitments to fiscal and monetary stimulus support a bull case, more clarity on inflationary risks, rising labor costs, the timeline for global COVID-19 vaccine adoption, and the post-COVID health of the global economy is needed for the allocation to stocks to increase. Against this backdrop, we feel that diversification across global assets could be a sensible approach for what we believe could be a bumpy ride.

We remain convinced that a broadly diversified portfolio, aligned with a long-term investment strategy, is the wisest course for those investors seeking retirement income. We remind you that it is important to maintain perspective and have realistic expectations about the future performance of your investment portfolio. As described in this report, financial markets can reverse suddenly, stumble along sideways, and reverse again. 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 markets like these, how long you have to save and invest, and your specific financial goals and risk tolerance.

^© 2022 Massachusetts Mutual Life Insurance Company (MassMutual^®), Springfield, MA 01111-0001. All rights reserved. www.MassMutual.com. Underwriter: MML Distributors, LLC. (MMLD) Member FINRA and SIPC (www.FINRA.org and www.SIPC.org), 1295 State Street, Springfield, MA 01111-0001. MMLD is a wholly-owned subsidiary of MassMutual. Investment advisory services provided to the Funds by MML Investment Advisers, LLC (MML Advisers), a wholly-owned subsidiary of MassMutual.

The information provided is the opinion of MML Advisers as of 1/1/2022 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.

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What are the investment approaches of the Funds that constitute the MML Allocation Series (the “Series”), and who is the Series’ investment adviser?

The MML Allocation Series comprises five Funds – each of which has a “fund of funds” structure. The five Funds in the Series are MML Conservative Allocation Fund, MML Balanced Allocation Fund, MML Moderate Allocation Fund, MML Growth Allocation Fund, and MML Aggressive Allocation Fund.

Each Fund seeks to achieve as high a total return over time as is considered consistent with prudent investment risk, preservation of capital, and recognition of the Fund’s stated asset allocation. Each Fund invests in a combination of U.S. domestic and international mutual funds (“MML Underlying Funds”) using an asset allocation strategy. MML Underlying Funds will include a combination of series of the MML Series Investment Fund and MML Series Investment Fund II (advised by MML Investment Advisers, LLC (“MML Advisers”), a wholly-owned subsidiary of Massachusetts Mutual Life Insurance Company (MassMutual), and may also include other, non-affiliated mutual funds. The MML Underlying Funds may invest in various asset classes, including equity securities, fixed income securities, and money market instruments. The Series’ investment adviser is MML Advisers.

Each Fund will normally invest most of its assets in MML Underlying Funds advised by MML Advisers; each Fund will normally invest no more than 10% of its assets in mutual funds not advised by MML Advisers (referred to here as “non-affiliated” funds).

Each Fund’s assets are allocated to its MML Underlying Funds according to an asset allocation strategy stated below.

How did each Fund perform during the 12 months ended December 31, 2021?

* Benchmark return

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The MML Conservative Allocation Fund, MML Balanced Allocation Fund, and the MML Moderate Allocation Fund all outperformed their respective Custom Indexes. All of the Funds underperformed the Russell 3000 Index by a wide margin. All five Funds in the Series outperformed the MSCI ACWI ex USA, and all significantly outperformed the Bloomberg U.S. Aggregate Bond Index for the full year.

MML Allocation Fund Series Custom Indexes

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

Investment adviser discussion of factors that contributed to the Funds’ performance

For the year ended December 31, 2021, the Series Funds delivered positive returns, as stocks outperformed fixed-income investments. Consequently, those Series Funds with higher equity allocations outperformed their Series Funds counterparts with higher fixed-income allocations.

Global stock investors experienced declining levels of volatility and strong positive returns in 2021. U.S. stocks rose steadily in the period, buoyed by the U.S. Federal Reserve Board’s commitment to low interest rates, additional rounds of fiscal stimulus, rising expectations for strong economic growth, and rebounding corporate earnings. Allocations across various asset classes intended to diversify risks in the Funds delivered mixed results. Foreign stocks in developed markets experienced gains during the year, aided by increasing economic activity, generous fiscal and monetary stimulus, and strong corporate earnings. Emerging-market stocks ended the year down, led by Chinese stocks that faced unexpected regulatory action and debt defaults in the Chinese real estate sector. U.S. bond investors generally experienced negative returns in the rising interest rate environment, fueled by an increase in economic growth expectations, heighted inflationary pressures, and a lessening of monetary and fiscal policy support. A bright spot in fixed income was U.S. high-yield bonds, which delivered positive returns for the year, buoyed by rising commodity prices, looser credit standards, and low default rates.

6

Manager selection detracted from the Series Funds’ overall performance in 2021. Weak performance by the MML Focused Equity, MML Blue Chip Growth, MML Mid Cap Value, and MML Strategic Emerging Markets Funds was a significant driver of underperformance. Strong results from the MML Fundamental Value, MML High Yield, MML Managed Bond, and MML Short-Duration Bond Funds helped overall performance.

Investment adviser outlook

As we enter 2022, we view the stock markets as extended and valuations high relative to market history. While the prospect of lower financing costs, strong economic and corporate earnings growth, and continued government commitments to fiscal and monetary stimulus support a bull case, more clarity on inflationary risks, rising labor costs, the timeline for global COVID-19 vaccine adoption, and the post-COVID health of the global economy is needed for the allocation to stocks to increase. Against this backdrop, we feel that diversification across global assets could be a sensible approach for what we believe could be a bumpy ride.

7

8

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

9

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

10

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

11

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

12

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

13

What is the investment approach of MML American Funds Growth Fund, and who is the Fund’s investment adviser?

The Fund seeks to provide investors with growth of capital through a “master feeder” relationship. (See page 234 of this report for information about the “master feeder” relationship.) The Fund invests all of its assets in Class 1 shares of the American Funds Insurance Series – Growth Fund (the “Master Growth Fund”), a series of the American Funds Insurance Series, a registered open-end investment company, managed by Capital Research and Management Company (Capital Research) with substantially the same investment objective. The Master Growth Fund invests primarily in common stocks and seeks to invest in companies that appear to offer superior opportunities for growth of capital. The Master Growth Fund may invest up to 25% of its assets in common stocks and other securities of issuers domiciled outside the United States. The Master Growth Fund may hold a portion of its assets in cash or cash equivalents. The Fund’s investment adviser is MML Investment Advisers, LLC (MML Advisers).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund returned 21.54%, significantly underperforming the 28.71% return of the S&P 500^® Index (the “benchmark”), which measures the performance of 500 widely held stocks in the U.S. equity market. The Fund also significantly underperformed the 27.60% return of the Russell 1000^® Growth Index, 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.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

Capital Research’s discussion of factors that contributed to the Fund’s performance

U.S. equities surged to new record highs in 2021, as the COVID-19 vaccine rollout helped businesses and the economy rebound from lockdowns in 2020. Strong corporate earnings and accommodative fiscal and monetary policies supported markets with relatively low volatility. The energy sector soared nearly 55%, rebounding from a more than 33% decline in 2020.

Massive stimulus measures helped boost investor confidence. A $1.9 trillion coronavirus relief package signed by President Biden in March included direct payments of up to $1,400 to individuals, extension of an unemployment insurance supplement, and expansion of the child tax credit.

For the year ended December 31, 2021, Fund holdings RingCentral (a provider of cloud-based communications and collaboration solutions for businesses) and a lower-than-benchmark position in Nvidia (an American semiconductor manufacturer), which outpaced the market in 2021, detracted from relative returns.

The Fund’s top contributors in relative terms were the consumer discretionary and consumer staples sectors. Specific Fund holdings that contributed to full-year performance included Tesla and ASML (a Dutch company that is a leading supplier to the semiconductor industry), both of which outpaced the broader market.

Capital Research’s outlook

As both the pandemic and economic growth appear poised to continue, Fund management is considering whether shortages of supplies and labor will continue to drive both prices and interest rates higher. Their view is that, for growth companies in this environment, the bigger the disconnect between sales and cash flow growth, the more vulnerable the securities are to declines in share price. Fund management and the Fund’s research team will continue to appraise this economic environment in search of attractive opportunities that could yield the potential for capital appreciation.

14

15

GROWTH OF $10,000 INVESTMENT - SERVICE CLASS I

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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

16

What is the investment approach of MML American Funds International Fund, and who is the Fund’s investment adviser?

The Fund seeks long-term capital growth of assets through a “master-feeder” relationship. (See page 234 of this report for information about the “master feeder” relationship.) The Fund invests all of its assets in Class 1 shares of the American Funds Insurance Series – International Fund (the “Master International Fund”), a series of the American Funds Insurance Series, a registered open-end investment company managed by Capital Research and Management Company (Capital Research) with substantially the same investment objective. The Master International Fund invests primarily in common stocks of companies domiciled outside the United States, including companies domiciled in emerging markets, that Capital Research believes have the potential for growth. The Master International Fund may hold a portion of its assets in cash or cash equivalents. The Fund’s investment adviser is MML Investment Advisers, LLC (MML Advisers).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund returned -1.96%, underperforming, by a wide margin, the 7.82% return of 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. The Fund significantly underperformed the 11.26% return of the MSCI EAFE Index, which measures the performance of the large- and mid-cap segments of developed markets, excluding the U.S. and Canada equity securities.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

Capital Research’s discussion of factors that contributed to the Fund’s performance

Global stocks rallied for the third year in a row in 2021, boosted by massive government stimulus measures and pent-up consumer demand. Market gains were tempered, at times, by worries about rising inflation, higher interest rates, and the spread of coronavirus variants. U.S. equities surged to new record highs, as the COVID-19 vaccine rollout helped businesses and the economy rebound from lockdowns in 2020. European stocks rallied, as widespread vaccine rollouts and massive government stimulus measures helped lift the eurozone economy out of a pandemic-induced downturn. Emerging-market stocks posted their weakest return since 2018, undercut by China’s economic slowdown and increased government intervention in the private sector.

With respect to the Fund itself, some investments within the health care and financials sectors hindered relative returns for the year ended December 31, 2021. Brazilian cloud technology platform StoneCo was a top detractor, as the Fund holding’s stock lagged the broader market.

Turning to the positive, the Fund’s investments in the energy and utilities sectors boosted relative returns for the year ended December 31, 2021. A higher-than-index position in ABN AMRO Bank contributed to returns, as the stock outpaced the wider market.

Capital Research’s outlook

Looking ahead, Fund management believes economic growth prospects are strong, particularly in developed markets, despite the continued rise in infection rates of COVID-19, as led by the omicron variant at year end. Fund management believes that, while emerging markets were hit hard during the pandemic, the worst may be behind them, and their view is that economic recovery in emerging markets seems to be progressing well. They also caution that a further rise in inflation may dampen the real returns of financial assets.

17

18

GROWTH OF $10,000 INVESTMENT - SERVICE CLASS I

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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

19

What is the investment approach of MML American Funds Core Allocation Fund, and who is the Fund’s investment adviser?

The Fund seeks to achieve as high a total return over time as is considered consistent with prudent investment risk, preservation of capital, and recognition of the Fund’s stated asset allocation. The Fund is a “fund of funds” and seeks to achieve its investment objective by principally investing in a combination of series of the American Funds Insurance Series (the “American Underlying Funds”), managed by Capital Research and Management Company (Capital Research), using a flexible asset allocation approach. The Fund’s investment adviser invests the Fund’s assets in a combination of U.S. domestic and international American Underlying Funds. As of the date of this report, it is expected that the American Underlying Funds will include Class 1 shares of the American Funds Insurance Series - The Bond Fund of America, the American Funds Insurance Series - Washington Mutual Investors Fund, the American Funds Insurance Series - Growth-Income Fund, and the American Funds Insurance Series - International Fund. The Fund’s investment adviser allocates the Fund’s assets among a variety of different asset classes through investing in American Underlying Funds in response to changing market, economic, and investment conditions. The Fund’s investment adviser is MML Investment Advisers, LLC (MML Advisers).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund returned 12.85%, significantly underperforming the 28.71% return of the S&P 500^® Index (the “benchmark”), which measures the performance of 500 widely held stocks in the U.S. equity market. The Fund outperformed, by a wide margin, the 7.82% return of the MSCI All Country World Index (ACWI) ex USA, 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. The Fund significantly outperformed the -1.54% return of the Bloomberg U.S. Aggregate Bond Index, 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). Finally, the Fund’s 12.85% return underperformed the 15.44% return of the Custom MML Core Allocation Index, which comprises the benchmark (55%), the Bloomberg U.S. Aggregate Bond Index (35%), and the MSCI ACWI ex USA (10%).

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

Capital Research’s discussion of factors that contributed to the Fund’s performance

The following paragraphs discuss the results of each of the Fund’s underlying portfolio components. Because the Fund invests in both stock- and bond-based portfolios, its overall performance may vary considerably from the broad market indexes listed above, which each measures the performance of a specific group of securities. These discussions focus on the results for each component and positioning versus each component’s main comparative index, not how the Fund as a whole performed or was positioned versus those indexes.

The American Funds Insurance Series – The Bond Fund of America (the “Bond Fund”) outperformed the Bloomberg U.S. Aggregate Bond Index (the “Index”) for the year, as fixed income markets were mixed in an environment where investors confronted higher inflation and prospects for tighter monetary policy. The Bond Fund’s relative performance benefited most from sector allocations, followed by security selection and duration positioning. The Bond Fund’s positions in Treasury Inflation Protected Securities (TIPS) and its modest position in high-yield bonds contributed to relative results. Duration and curve positioning within MBS were detractors over the reporting period.

The American Funds Insurance Series – Washington Mutual Investors Fund (the “Income and Growth Fund”) underperformed its benchmark in 2021, despite the surge of U.S. equities to new record highs as the COVID-19 vaccine rollout helped businesses and the economy rebound from lockdowns in 2020. The Income and Growth Fund’s investments within the materials sector dragged on results. Specifically, media company Comcast hindered returns, as its stock lagged the broader market. Conversely, the energy and health care sectors were top contributors to relative returns. Information technology firm Broadcom was among the Income and Growth Fund’s top contributors, with a higher-than-benchmark position and returns that outpaced the broader market.

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The American Funds Insurance Series – Growth-Income Fund (the “Growth-Income Fund”) underperformed its benchmark for the year, in an environment where strong corporate earnings and accommodative fiscal and monetary policies supported markets with relatively low volatility. During the year, the Growth-Income Fund’s information technology and real estate sector investments were a drag on relative returns. In particular, an investment in media firm Comcast hindered results. On the other hand, the Growth-Income Fund’s investments in the energy and communication services sectors contributed to relative returns. With respect to the Growth-Income Fund’s holdings, a higher-than-benchmark position in information technology firm Broadcom was a top contributor.

The American Funds Insurance Series – International Fund (the “International Fund”) underperformed the MSCI ACWI ex USA (the “Index”) for the year, as global stocks rallied for the third year in a row, boosted by massive government stimulus measures and pent-up consumer demand. With respect to the International Fund, some investments within the health care and financials sectors hindered relative returns for the year. Among individual International Fund holdings, Brazilian cloud technology platform StoneCo was a top detractor, as its stock lagged the broader market. On the other hand, the International Fund’s investments in the energy and utilities sectors boosted relative returns for the year. With respect to specific holdings, a higher-than-Index position in ABN AMRO Bank contributed to returns, as the stock outpaced the wider market.

Capital Research’s outlook

With respect to fixed income, Fund management believes the U.S. economy has the potential to maintain momentum on the back of strong consumer spending and business investment, even amid elevated inflation and the prospect of the U.S. Federal Reserve Board (the “Fed”) raising interest rates early in 2022. Although at year end, the Bond Fund was positioned toward further economic growth, Fund management anticipates a high level of uncertainty and a rise in market volatility in 2022.

With respect to U.S. equities, looking ahead, Fund management is keeping a close watch on monetary policy, the path of the pandemic, inflation, and the resulting implications for the U.S. economy. In their view, a further reduction in COVID-19 restrictions would be positive for economic activity in 2022. On the other hand, they note that higher inflation is causing the Fed to plan for interest rate hikes in 2022, which could bring additional volatility to equity markets.

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22

GROWTH OF $10,000 INVESTMENT - SERVICE CLASS I

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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

23

What is the investment approach of MML Blue Chip Growth Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital growth. Income is a secondary objective. Under normal circumstances, the Fund invests at least 80% of net assets (plus the amount of any borrowings for investment purposes) in the common stocks of large- and medium-sized blue chip growth companies. The Fund’s subadviser currently defines blue chip growth companies to mean firms that, in its view, are well-established in their industries and have the potential for above-average earnings growth. The Fund’s subadviser is T. Rowe Price Associates, Inc. (T. Rowe Price).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 16.34%, significantly underperforming the 27.60% 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. In addition, the Fund underperformed, by a wide margin, the 28.71% return of the S&P 500^® Index, 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 December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, less-than-favorable stock selection was the primary driver of the Fund’s relative underperformance. Fund holdings within the information technology, consumer discretionary, and communication services sectors were the primary detractors, while Fund holdings in the financial and industrial and business services sectors were the largest contributors.

Within information technology, Fund holding Global Payments was a major detractor, as better-than-expected top- and bottom-line results were not enough to shake the disruption narrative that has recently plagued legacy payment processors. Fund management eliminated its position in Global Payments in favor of more attractive opportunities. The consumer discretionary sector also detracted on a relative basis, due to unfavorable stock choices and the Fund’s underweight position in Tesla. Shares of Tesla climbed higher during 2021, as the company successfully ramped production, amid a global supply chain disruption, to meet strong electric vehicle (EV) demand. Profitability also benefited from a mix of higher-margin Model Y deliveries, particularly in China. Nevertheless, Fund management maintained an underweight position in Tesla, based on what they believe is a dislocation between valuation and fundamentals – and concerns over the emergence of legitimate competition on the horizon. Communication services further hampered relative results, as some Fund holdings within the sector struggled. For example, continued waves of regulatory pressure weighed on shares of Tencent Holdings (a Chinese multinational technology and entertainment conglomerate and holding company), as new guidelines were introduced to combat anticompetitive practices and step up oversight of video game approvals.

On the other side of the ledger, Fund holdings in the financial sector contributed the most to the Fund’s full-year relative performance. For example, shares of Goldman Sachs benefited from vigorous capital markets activity, along with notable traction within their consumer and wealth management businesses. The industrial and business services sector also bolstered relative returns, driven by a favorable underweight allocation, although that was moderately offset by underperforming Fund holdings within the sector.

Subadviser outlook

After back-to-back years of strong performance across most equity and credit sectors, Fund management believes that global markets face more uncertain prospects in 2022. In their view, investors will need to use greater selectivity to identify potential opportunities. Higher inflation, a shift toward monetary tightening, and new coronavirus variants all pose potential challenges for economic growth and earnings – at a time when, in Fund management’s view, valuations appear elevated across many asset categories. Fund management believes that as governments and central banks withdraw the massive stimulus applied during the pandemic, economic growth has the potential to slow sharply. But in their view, slower growth doesn’t necessarily mean low growth. Fund management feels that a number of tailwinds could sustain the economic recovery in 2022, including strong consumer and corporate balance sheets.

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25

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

26

What is the investment approach of MML Equity Income Fund, and who is the Fund’s subadviser?

The Fund seeks dividend income and long-term capital growth by investing primarily in common stocks, with an emphasis on large-capitalization companies that have a strong track record of paying dividends or that the Fund’s subadviser believes to be undervalued. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in common stocks. The Fund’s subadviser is T. Rowe Price Associates, Inc. (T. Rowe Price).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 25.58%, outperforming the 25.16% 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.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

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

For the year ended December 31, 2021, favorable sector allocation and security selection were both primary drivers of the Fund’s relative outperformance. The financial, information technology, and communication services sectors were the largest relative contributors, while the consumer discretionary and industrial and business services sectors were the most significant relative detractors.

Fund holdings within the financial sector were the primary relative contributors: Shares of Wells Fargo ended higher after continued consumer credit resilience and the U.S. Federal Reserve Board’s (the “Fed”) “green-lighting” banks to resume returning capital to shareholders in the second half of the year. Despite shares being impacted by negative headlines related to the company’s deficiencies in its lending loss mitigation program, Wells Fargo delivered strong loan growth figures late in the period, which lifted the price of its shares.

Fund holdings in the information technology sector, such as Applied Materials, also aided relative performance. Applied Materials rose as shares continued to benefit from cyclical strength within the industry and robust semiconductor demand over the year. The communication services sector also contributed to relative returns due to the Fund’s underweight allocation to the sector, relative to the benchmark.

Conversely, Fund holdings in the consumer discretionary sector detracted from relative performance. Shares of Las Vegas Sands finished lower due to continued coronavirus-related travel restrictions imposed by the Macanese government. Fund holdings in the industrial and business services sector also hindered relative performance. GE, for example, underperformed the broader sector, following a muted reaction to the company’s proposed plan to split into three separate companies. Additionally, there was growing concern within market investors regarding the impact the omicron variant could have on the aviation industry.

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 warrants during the reporting period contributed slightly to the Fund’s performance.

Subadviser outlook

Market concerns surrounding the coronavirus were met with an aggressive and coordinated fiscal and monetary policy response in recent periods. Moving forward, all eyes remain on the trajectory of both the virus and government policy. Given this duality, Fund management expects a choppy market throughout 2022, with a focus on potential missteps by the Fed. Fund management believes that while fundamentals remain strong, the equity market is relatively expensive, particularly on the growth side. However, low bond yields mean that there are few alternatives to equities. Fund management believes that, for markets to continue their ascent, they will need to climb a wall of worry consisting of pandemic dynamics, inflation, and labor shortages. Fund management believes that the intensity of each concern could have a strong bearing on equity market returns in 2022.

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28

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

29

What is the investment approach of MML Equity Index Fund, and who is the Fund’s subadviser?

The Fund’s investment objective is to provide investment results that correspond to the price and yield performance of publicly traded common stocks in the aggregate as represented by the S&P 500^® Index* (the “Index”). Under normal circumstances, the Fund invests at least 80% (and, typically, substantially all) of its net assets (plus the amount of any borrowings for investment purposes) in the equity securities of companies included within the Index. The Fund’s subadviser is Northern Trust Investments, Inc. (NTI).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class I shares returned 28.19%, underperforming the 28.71% return of the Index, 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 December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

Generally, the Fund’s underperformance versus the Index was mainly attributable to the impact of fees and expenses necessary for the management and operation of the Fund. The Index is not subject to fees or expenses and it is not possible to invest directly in the Index.

For the year ended December 31, 2021, energy and real estate were the strongest-performing sectors within the Index, returning 54.74% and 46.20%, respectively. The utilities and consumer staples sectors exhibited the worst performance, returning 17.63% and 18.63%, respectively.

During 2021, U.S. equities performed exceptionally well and finished the year near all-time highs. For the third consecutive year, U.S. equities posted double-digit gains. The first quarter of 2021 experienced continued rising interest rates and inflation concerns, which weighed on equity returns, but inoculation, economic reopening, and stimulus tailwinds proved powerful enough to result in modestly positive returns. During the second quarter, government bond yields settled, and U.S. equities – growth stocks in particular – rebounded from mid-quarter pressure. U.S. equities were flat in the third quarter due to investor concerns in September that focused on peak growth, inflation, and unwinding stimulus. U.S. equities finished the fourth quarter strongly, as investors focused on solid consumer spending and employment data, while digesting stubbornly high inflation figures. Increasing inflation expectations, along with strong economic data, caused the U.S. Federal Reserve (the “Fed”) to increase its pace of asset purchase tapering and pull forward expectations of interest rate hikes.

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 equity futures to equitize/gain market exposure for relatively small amounts of cash in the Fund in order to minimize the uninvested cash balances and reduce the impact of any cash drag. The impact of derivatives on Fund performance was minimal.

Subadviser outlook

Looking ahead, Fund management believes that uncertainty is likely to prevail concerning inflation, rising rates from the Fed, and the U.S. mid-term elections. While Fund management believes that the U.S. economy could slow in 2022, their belief is that the outlook still appears positive.

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31

GROWTH OF $10,000 INVESTMENT - CLASS I

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

32

What is the investment approach of MML Focused Equity Fund, and who is the Fund’s subadviser?

The Fund seeks growth of capital over the long-term by investing primarily in equity securities of U.S. companies that the Fund’s subadviser believes are financially sound, valued conservatively by the market, and have improving prospects. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities. The Fund’s subadviser is Wellington Management Company LLP (Wellington Management).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class II shares returned 22.25%, underperforming the 26.45% return of the Russell 1000^® Index (the “benchmark”), which measures the performance of the large-cap segment of U.S. equity securities. It is a subset of the Russell 3000^® Index and includes approximately 1000 of the largest 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 December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, sector allocation, a result of the Fund’s bottom-up stock selection process, drove relative underperformance. This was due to the Fund’s overweight (relative to the benchmark) allocation to the consumer staples sector, its underweight position in information technology, and its lack of exposure to the energy sector. These factors were partially offset by the Fund’s lack of exposure to the communication services and utilities sectors, as well as its overweight allocation to the financial sector.

With respect to specific Fund holdings, top relative detractors for the period included Medtronic (health care) and Colgate-Palmolive (consumer staples). Shares of Medtronic, a developer of therapeutic and diagnostic medical products, fell during the reporting period. In the fourth quarter of 2021, the headquarters of Medtronic’s Diabetes business received a warning letter from the U.S. Food and Drug Administration (FDA), which prompted the company to revise guidance downward for its Diabetes segment, causing the share price of the stock to fall. The share price of Colgate-Palmolive, a manufacturer of oral, personal, and household products, was weighed down after management lowered full-year guidance, citing significant raw material and logistics cost headwinds that they expected to continue in the second half of 2021.

Fund holdings that were among the top relative contributors for the period were both from the financial sector –Marsh & McLennan and American Express. Not owning benchmark constituent Amazon (consumer discretionary) also contributed. Shares of insurance company Marsh & McLennan rose during the period, benefiting from strength in its risk and insurance services business as well as its e-consulting business. Globally integrated payments company American Express reported strong earnings throughout the period on the back of credit reserve releases. Increased consumer spending contributed to accelerating momentum in its core business and improving credit performance.

Subadviser outlook

Looking forward into 2022, Fund management notes that there is heightened investor concern over inflation and interest rates. Markets have long been driven by a narrow list of technology stocks, boosted by high risk tolerance, strong retail support, and a desire for perceived growth. In Fund management’s view, growth stocks seem to be fading in the face of inflation/rate worries, and consequently, value stocks seem to be well-positioned. Fund management believes the emerging investment backdrop has the potential to benefit the Fund’s investments. With respect to inflation, Fund management thinks that Fund holdings could be well-positioned to navigate the challenges – as they are strongly profitable, are steady compounders that grow over time, and generally have relatively little debt, making rate hikes less of a threat. Fund management believes this has the potential to result in steady financial results, which ultimately produce strong and predictable dividend growth. At the end of the period, the Fund held its largest overweight allocations in the consumer staples and health care sectors, and was most underweight in the information technology sector.

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34

GROWTH OF $10,000 INVESTMENT - CLASS II

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

35

What is the investment approach of MML Foreign Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return by investing primarily in common stocks of companies listed on foreign securities exchanges. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in investments of issuers located outside of the U.S., including those in emerging markets. Under normal market conditions, the Fund invests in equity securities of foreign companies representing at least three countries other than the United States. Although the Fund may invest in companies of any size as measured by assets, sales, or market capitalization, the Fund will tend to focus on larger, more seasoned or established companies. The Fund’s subadviser is Thompson, Siegel & Walmsley LLC (TSW).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 13.04%, outperforming the 11.26% return of the MSCI EAFE Index (the “benchmark”), which measures the performance of the large- and mid-cap segments of developed markets, excluding the U.S. and Canada equity securities.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, on a regional basis, Japan contributed the most to the Fund’s performance, with Toshiba Corporation and Sony Group Corporation among the top Fund holdings. Multinational conglomerate Toshiba performed well after taking steps to address corporate governance issues and announcing its intention to split into three parts. Electronics company Sony Corporation reported a series of strong results across its operating segments and raised its full-year guidance. The company’s games segment performed well, following the release of PlayStation 5, and its music segment also performed well, garnering a higher valuation following the initial public offering (IPO) of Universal Music Group.

On the downside, the Fund’s small allocation to emerging markets detracted the most from relative returns for the year. The Fund’s emerging-market exposure to South Korean electronics producer Samsung hampered its performance, as shares of the Fund holding trailed its benchmark – due to analyst concerns over a declining memory chip cycle outweighing the stock’s solid operating performance.

On a sector basis, consumer discretionary and financial were the top contributors to the Fund’s relative returns. Fund holdings Sony Group Corporation and Entain PLC were among the top performers in consumer discretionary. In addition to Sony’s success (noted above), U.K. gambling company Entain PLC performed well after receiving multiple takeover offers from gaming peers MGM and DraftKings. Orix Corporation and Macquarie Group Limited were two Fund holdings that performed well in the financial sector.

Fund holdings in the communication services sector detracted from relative returns for the year. Within that sector, Ubisoft Entertainment SA and Nintendo Co., Ltd. were laggards. These two companies were COVID-19 beneficiaries and, despite their improving fundamentals and strong growth outlooks, investors’ focus rotated toward companies more exposed to economies reopening. French video game creator Ubisoft underperformed as its management lowered its full-year guidance due to the postponement of certain content releases from 2021 to 2022. Shares of Nintendo declined after the company underwhelmed analysts with its recent results. Fund holdings in the health care sector also detracted from relative returns. Dutch health care technology company Philips N.V. underperformed after reporting mixed results due to the recall of certain legacy sleep care products. German health care company Fresenius underperformed despite reporting satisfactory results. The company saw improvements in its hospital division and specialized medical products division; however, a large portion of its business revolves around necessary, but elective, procedures – many of which have been postponed in the COVID-19 environment.

36

Subadviser outlook

Fund management believes the current situation is tailor-made for active management. 2022 has begun with reasons for pessimism about the outlook for stocks: in Fund management’s view, economic growth could moderate as pent-up demand from the pandemic era is exhausted, central banks are pivoting away from their expansionary policies over inflation concerns, COVID-19 appears to be heading toward endemic status, and companies are dealing with rising input costs and balky supply chains. Despite all this, Fund management finds cause for optimism at the company level. In their view, the best firms have shown that powerful business models and management acumen engender fundamentally positive results and shareholder returns, despite the headwinds, and that companies with flexible balance sheets, variable costs structures, and the power to pass price increases to customers could continue to prosper. Fund management believes that valuations appear reasonable, especially in markets like Germany, Japan, and the U.K.

37

38

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

39

What is the investment approach of MML Fundamental Equity 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. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities. The Fund’s subadviser is Invesco Advisers, Inc. (Invesco).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class II shares returned 27.67%, underperforming the 28.71% return of the S&P 500^® Index (the “benchmark”), which measures the performance of 500 widely held stocks in the U.S. equity market. The S&P 500 Index more closely represents the Fund’s investment strategy.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, stock selection within the communication services, energy, and consumer staples sectors was the primary driver of the Fund’s underperformance. This was partially offset by stronger stock selection in the health care, real estate, and information technology sectors.

Not holding top-performing stock NVIDIA was the largest relative detractor from the Fund’s performance for the year. Fund holdings that were top detractors from relative results included Fiserv, Amazon, and Verizon. Fiserv, a financial technology company that provides payments services, was under pressure due to a more difficult competitive environment for the company’s merchant acquisition business. Additionally, there have been concerns that non-traditional banks will negatively impact the traditional money center banks – and by extension, Fiserv, as a technology provider. Amazon traded mostly flat during the year, but was a key relative detractor in the context of significant gains for the benchmark. Amazon’s modestly positive total return came after experiencing significant gains in 2020 (as a stay-at-home beneficiary of the pandemic), which led to tougher comparisons in 2021. Verizon underperformed, along with the telecommunications group in general, as those stocks tend to be more defensive and value oriented, while the benchmark experienced strong gains led by the growth sub-segment of the market. Additionally, the company dealt with COVID-related retail store restrictions, which limited the pool of potentially switching subscribers, while AT&T simultaneously used aggressive pricing to defend its subscriber base.

Fund holdings that were top contributors to relative performance included Applied Materials, Capital One, and Prologis. Applied Materials (and their semiconductor equipment competitors in general) benefited from strong secular demand for semiconductors, which has supported positive earnings estimate revisions. Capital One, along with financial stocks overall, outperformed, as the U.S. continued its path to reopening. Additionally, the company benefited from a pick-up in travel, hotel bookings, and dining, all of which helped drive credit card growth. Further, consumers continued to benefit from the aggressive stimulus and forbearance programs that helped limit delinquencies and charge-offs. Prologis, an industrial real estate investment trust (REIT), continued to post strong tenant demand and same-property rent growth, driven by its customers’ need to expand and strengthen supply chains to support the growth of e-commerce.

Subadviser outlook

The U.S. economy is experiencing a sustained recovery from the COVID-induced recession, as reopening builds steam. While the omicron variant caused some mild reversals in return-to-office plans and paused normalization, it has not materially slowed economic growth. Fund management believes COVID-19 appears to be moving from a pandemic to a less-severe endemic disease. Stocks have experienced significant gains over the past two years, while underlying earnings have grown roughly in line with stock prices. Interest rates remained low at year end, but in Fund management’s view, long-term rates bear watching. They continue to seek companies with competitive advantages and skilled management teams that are out-executing their peers.

40

41

GROWTH OF $10,000 INVESTMENT - CLASS II

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

42

What is the investment approach of MML Fundamental Value Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return by investing primarily in equity securities of issuers that the Fund’s subadviser believes are undervalued. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities, with a focus on companies with large market capitalizations (which the subadviser believes are generally above $1 billion). The Fund’s subadviser is Boston Partners Global Investors, Inc. (Boston Partners).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class II shares returned 30.02%, outperforming the 25.16% 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.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, stock selection was the primary driver of the Fund’s outperformance relative to the benchmark, led by Fund holdings in the information technology, communication services, and industrial sectors. Within information technology, semiconductor equipment companies Applied Materials, Lam Research, and KLA benefited from increased capital spending by manufacturers, as higher demand resulted in supply shortages. In communication services, Fund holdings in internet-related companies Alphabet (the parent company of Google) and Meta Platforms (formerly Facebook) added value, as both companies continued to report strong earnings. The Fund’s avoidance of underperforming benchmark constituents AT&T, Verizon, Comcast, and Disney also aided relative returns for the year. Within the industrial sector, heavy equipment manufacturer Deere, elevator manufacturer Otis, and equipment rental company United Rentals were three Fund holdings that benefited from strong orders and better-than-expected margins. Sector allocation also contributed positively to the Fund’s full-year performance, due to overweight allocations, relative to the benchmark, to the energy and financial sectors, and underweight allocations to the communication services and consumer staples sectors.

Stock selection detracted within the materials and financial sectors during the one-year period. In materials, Fund holdings of gold miners Yamana and Kinross lagged as gold prices declined in 2021, while the prices of other commodities increased considerably – resulting in less relative earnings momentum for gold companies. In the financial sector, the Fund’s overweight position in auto insurer Progressive did not keep pace with the market and detracted on a relative basis, as pricing within the industry was more competitive than expected. The Fund’s overweight allocations to health care and information technology and its underweight allocation to real estate detracted from relative performance.

During the year, the Fund increased its exposure to the energy and information technology sectors and reduced its exposure to the financial sector. In energy, the Fund added Canada-based exploration and production company Cenovus, whose new management team began focusing on return on investment and cash flow allocation. Within information technology, the Fund added fintech company Global Payments, which trades at an attractive valuation relative to its historical valuations, with accelerating earnings resulting from the fact that credit card transactions continued to rebound with the economy. In the financial sector, the Fund reduced its exposure by selling auto insurer Progressive. The Fund also trimmed its allocations to outperformers Bank of America and AIG – to rebalance those position sizes to appropriate levels.

Subadviser outlook

Fund management will continue to focus on finding investments that have not only attractive valuation characteristics and solid business fundamentals, but also improving business momentum and catalysts that Fund management believes could help drive stock prices higher. In their view, the global economy could continue to see above-trend economic growth in 2022. Historically, strong gross domestic product (GDP) and corporate earnings, rising inflation, and increasing interest rates have benefited more economically sensitive value stocks over expensive growth favorites. With current valuation spreads between value and growth stocks very wide, Fund management believes the portfolio is well positioned to take advantage of these opportunities going forward.

43

44

GROWTH OF $10,000 INVESTMENT - CLASS II

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

45

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

The Fund seeks long-term capital appreciation by investing primarily in the equity securities of U.S. and foreign companies, including companies in developed and emerging markets. The Fund may invest a significant percentage of its assets in issuers in a single industry, sector, country, or region. The Fund’s subadviser is Massachusetts Financial Services Company (MFS).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class I shares returned 17.32%, underperforming the 21.82% return of the MSCI World Index (the “benchmark”), which measures the performance of the large- and mid-cap segments of world equity securities.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

Security selection within the information technology sector was the primary factor that detracted from the Fund’s relative performance for the year ended December 31, 2021. Within the sector, not owning shares of software giant Microsoft, computer graphics processor maker NVIDIA, and personal electronics maker Apple detracted from the Fund’s relative results. The Fund’s overweight allocation, relative to the benchmark, to global provider of banking and payment technologies Fidelity National Information Services and global payments technology company Visa^® also hampered the Fund’s relative performance.

Stock selection in the communication services sector also detracted from the Fund’s relative returns – as its avoidance of technology company Alphabet (the parent company of Google), as well as overweight allocations to cable services provider Comcast and diversified entertainment company Walt Disney, hindered results. Fund holdings in other sectors also negatively impacted relative returns. These included the Fund’s overweight positions in medical device maker Medtronic, and diversified technology and manufacturing company Honeywell International.

Turning to the positive, security selection within the consumer discretionary sector contributed to the Fund’s relative performance for the year. Within this sector, avoiding poor-performing internet retailer Amazon and an overweight allocation to luxury goods company Compagnie Financière Richemont (Switzerland) boosted relative results.

Fund holdings in the financial sector also helped relative returns, led by overweight positions in financial services providers Charles Schwab and Goldman Sachs Group. Elsewhere, the Fund’s overweight positions in IT servicing firm Accenture, life sciences supply company Thermo Fisher Scientific, railroad company Kansas City Southern, electrical distribution equipment manufacturer Schneider Electric (France), premium drinks distributer Diageo (United Kingdom), and pharmaceutical company Merck KGaA (Germany) positively impacted relative performance, as these Fund holdings were all standout performers for the year.

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. During the year, the Fund’s use of warrants contributed modestly to its performance.

Subadviser outlook

In Fund management’s view, the macro environment is changing. Following a decade of falling interest rates, they believe we could be approaching the point of “regime change.” Central bankers have started to rein in and taper their asset purchases and have begun raising interest rates to offset inflationary pressures. This turn in the direction of monetary policy has implications for all asset classes. Much of the “buy case” for equities has rested on their offer of relative value compared to low-yielding bonds. For a while, equities have not looked cheap to Fund management in absolute terms. Their view is that equity valuations in some sectors look stretched and risks abound – including heightened inflation, fading stimulus, higher taxes, trade wars, potential central bank policy mistakes, new COVID variants, and ongoing worldwide geopolitical risks. With profit margins at all-time highs, Fund management believes that investors should prepare for the potential that lower returns are ahead, as they view that it may be unlikely that the spectacular returns of the past decade will be repeated.

46

47

GROWTH OF $10,000 INVESTMENT - CLASS I

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

48

What is the investment approach of MML Growth & Income Fund, and who is the Fund’s subadviser?

The Fund seeks capital appreciation and income by investing, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities and equity-related securities, including convertible securities, preferred stocks, options, and warrants, of U.S. companies with market capitalizations at the time of purchase greater than $1 billion. The Fund’s subadviser is Massachusetts Financial Services Company (MFS).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 27.14%, underperforming the 28.71% 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 December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, security selection in the information technology sector detracted from the Fund’s relative performance. Within this sector, not owning shares of computer graphics processor maker NVIDIA, and overweight allocations, relative to the benchmark, in global provider of banking and payment technologies Fidelity National Information Services and global payments technology company Visa^®, held back relative returns.

Stock selection in both the health care and real estate sectors also weakened the Fund’s relative results. Within the health care sector, overweight positions in medical device maker Medtronic and medical technology company Becton, Dickinson and Co. held back relative performance. Fund holdings in other sectors that hindered relative performance included overweight positions in video game maker Electronic Arts, diversified technology and manufacturing company Honeywell International, and cable services provider Comcast. Additionally, not owning electric vehicle manufacturer Tesla and Fund holding Danone (France), a food processing company that is not a benchmark constituent, further detracted from the Fund’s relative results.

On the positive side, stock selection in the consumer discretionary and financial sectors contributed to the Fund’s relative performance. Within the consumer discretionary sector, an underweight position in internet retailer Amazon and an overweight allocation to specialty rural lifestyle retailer Tractor Supply boosted relative returns. Within the financial sector, Fund holdings that contributed to performance included global alternative asset manager Blackstone Group (which is not in the benchmark) and an overweight position in securities exchange services provider NASDAQ. The Fund’s security selection in the communication services sector also helped relative results, led by an overweight position in technology company Alphabet (the parent company of Google) and not owning shares of diversified entertainment company Walt Disney.

Stock selection in other sectors that contributed to relative performance included clinical research company ICON (Ireland), a Fund holding that is not represented in the benchmark; not owning shares of digital payment technology developer PayPal; and overweight positions in two Fund holdings – pharmaceutical company Eli Lilly and oil and gas company ConocoPhillips.

Subadviser outlook

Looking forward, Fund management feels that tighter monetary policy in response to inflation seems likely. While investors typically view rising interest rates as unfavorable to equities, data from Credit Suisse indicates that stock returns remained robust in the months leading up to and following the first rate increase. In looking at the past four cycles (1994, 1999, 2004 and 2015), the S&P 500 gained 9.5% in the 12 months prior to the first rate hike and 26% over the subsequent three years. Market weakness from higher rates tends to occur later in the cycle, when tighter policy flattens or inverts the yield 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.) While the possibility of higher returns exists, Fund management believes that investors should be prepared for the potential of more subdued market returns than we have seen over the past three years – and should understand that a maturing earnings cycle may lead to more volatility. Ultimately, given a potential mix of tighter financial conditions, slowing economic growth, and higher volatility, Fund management believes investors could be more selective in the next phase of the market and may start to lean toward higher-quality and more defensive issues.

49

50

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

51

What is the investment approach of MML Income & Growth Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return and current income by investing primarily in equity securities of issuers that the Fund’s subadviser believes are undervalued. Although the Fund may invest in companies of any size, the Fund will tend to focus on companies with large market capitalizations (which the Fund’s subadviser believes are generally above $2 billion). The Fund’s subadviser is Barrow, Hanley, Mewhinney & Strauss, LLC (Barrow Hanley).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 26.27%, outperforming the 25.16% 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.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

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

For the year ended December 31, 2021, stock selection within the industrial, information technology, and consumer discretionary sectors was the primary driver of the Fund’s relative outperformance. Conversely, the Fund’s stock choices within the energy, real estate, and health care sectors detracted from relative performance.

The Fund benefited from holdings such as theme park operator SeaWorld Entertainment. While 2021 attendance figures were slightly below 2019 levels, the company’s parks continued to post exceptionally strong performance, given increases in per-capita spending and fairly dramatic reductions in operating expenses versus pre-pandemic levels.

Another Fund holding, home improvement retailer Lowe’s, benefited from a 16% year-over-year increase in same-store sales – and has shown impressive traction in its efforts to close the performance gap versus its largest competitors. Additionally, Wells Fargo & Company, Hess Corporation, and CVS Health were three Fund holdings that were among the top contributors to relative performance for the year.

Several holdings hampered the Fund’s full-year results. Cable television provider Altice USA was the largest detractor from relative performance. Altice underperformed in the second half of 2021 as its CEO disclosed disappointing internet subscriber trends at a conference in September. Casino and entertainment company Las Vegas Sands Corp. detracted from relative performance, as the recovery in Macau remained muted due to government-enforced travel restrictions arising from its zero-tolerance COVID-19 policy. In Fund management’s view, China has been overly conservative in managing the pandemic and has been slow to ease travel restrictions to Hong Kong and Macau. Other Fund holdings that detracted from relative performance included Medtronic, Comcast Corporation, and BWX Technologies.

Subadviser outlook

Fund management notes that, by nearly every metric, valuation disparities between growth and value reached new highs in late 2021 – an enormous feat in their view, considering that growth was already at all-time-highs in late 2020. Value stocks fell back into the bottom few percentiles of “cheapness” (meaning the least expensive), while growth’s recent performance run left it further elevated and more susceptible to inflation and interest rate movements. At year end, growth stocks were primarily valued on a price-to-sales (P/S), rather than a price-to-earnings (P/E), basis, likely due to the fact that a meaningful percentage of those stocks have no earnings. The pile of broken “unicorn” stocks grows each week, as they are beginning to show signs of “wear and tear,” and, in Fund management’s view, they have much farther to fall when fundamentals – based on actual earnings and dividends, not top line sales – come to the fore.

Fund management believes the primary conditions needed for a sustained, impactful value run are not only present, but also more pronounced than they were when the value run began. Higher inflation, rising interest rates, and reasonable economic growth are aligned in a way that Fund management has rarely seen in its 43-year history.

52

53

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

54

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

The Fund seeks long-term capital growth by investing, under normal circumstances, at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of non-U.S. companies located in non-U.S. markets throughout the world, including emerging markets. The Fund may invest up to 25% of its total assets in equity securities of issuers in emerging markets. Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stocks, depositary receipts, rights, and warrants of issuers of any size. As of December 31, 2021, the Fund’s two subadvisers are Harris Associates L.P. (Harris), which managed approximately 34% of the Fund’s portfolio; and Massachusetts Financial Services Company (MFS), which managed approximately 66% of the Fund’s portfolio. Effective November 1, 2021, MFS was added as a subadviser of the Fund.

As previously disclosed to shareholders on November 2, 2021, the Fund’s 80% test relating the Fund’s name to its principal investments is being changed as follows on or about January 1, 2022: Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of foreign companies, including companies located in Europe, Latin America, and Asia.

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Class II shares returned 11.77%, underperforming the 12.62% return of the MSCI World Index ex USA (the “benchmark”), which measures the performance of the large- and mid-cap segments of world, excluding U.S. equity securities.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the Harris component of the Fund, Fund management’s bottom-up approach in selecting stocks, country, and sector allocations is a result of their stock selection process. For the year ended December 31, 2021, with respect to country performance relative to the benchmark, both stock selection and country weightings detracted from results. Relative sector performance was negatively impacted by stock selection, while sector weightings contributed to overall results. From a geographic perspective, the U.K. and Japan produced the best relative performance for the year, due to a combination of positive stock selection and weightings discrepancies relative to the benchmark. Fund component holdings in China detracted the most from relative performance. Germany was the next-largest relative detractor, which stemmed from poor stock selection effects along with a greater-than-benchmark weighting. However, Germany supplied a positive absolute return, led by consumer discretionary company Daimler, which delivered the country’s largest positive absolute return. From a sector perspective, communication services generated the best relative performance. In particular, media and entertainment companies WPP and Publicis Groupe were two Fund component holdings that were top contributors. The materials sector produced the next-best relative return for the year. The consumer discretionary sector detracted the most from relative results, partly due to two Fund component holdings, as Chinese-based consumer discretionary companies Vipshop Holdings and Alibaba Group delivered the largest negative returns. Derivatives can be used for hedging, speculation, or both. As of year end, approximately 15% of the Fund component’s exposure to the Swiss franc was hedged. Currency hedges contributed slightly to the Fund component’s performance for the year.

For the time that MFS served as subadviser to the Fund (beginning November 1, 2021), stock selection in the consumer discretionary sector contributed to the Fund component’s relative performance. Within this sector, overweight positions in luxury goods company Richemont (Switzerland), food catering company Compass Group (United Kingdom), and automotive component manufacturer Denso (Japan) benefited relative returns. Stock selection and an overweight position in the consumer staples sector also supported relative returns. Within this sector, the MFS component’s overweight positions in premium drinks distributor Diageo (United Kingdom) and global food company Nestle (Switzerland) helped relative performance. Fund component holdings that weakened relative returns included overweight positions in technology company Koninklijke Philips NV (Netherlands), electronics company Hitachi (Japan), insurer AIA Group (Hong Kong), medical products and equipment manufacturer Terumo (Japan) and human resources and employment services provider Randstad (Netherlands). During the reporting period, the Fund component’s relative currency exposure, resulting primarily from differences between the Fund component’s and the benchmark’s exposures to holdings of securities denominated in foreign currencies, contributed to relative performance.

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Subadviser outlook

Harris notes that global markets moved higher early in 2021, as vaccines reached more people worldwide. Despite energy suppliers’ rush to ramp up production to meet growing demand, a supply shortage and bottlenecks at major U.S. ports sent U.S. oil prices in excess of $85 per barrel for the first time since 2014. As previously announced, the U.S. Federal Reserve Board (the “Fed”) slowed its pace of asset purchases in November. The tapering came as the rate of inflation in the U.S. quickened to 6.8% versus the year-ago period. The Fed’s plan now calls for three rate hikes each in 2022 and 2023. The Bank of Japan and the European Central Bank echoed similar sentiments as they also left interest rates unchanged, while the Bank of England raised its main interest rate from 0.1% to 0.25% following a surge in U.K. inflation to a 10-year high of 5.1% annual growth in November. With seemingly constant uncertainty in politics, economics, and market sentiment, Harris plans to focus on finding undervalued and well-managed companies that have the potential to benefit from economic tailwinds, while proving capable of weathering difficult environments.

MFS observes that the macro environment may be changing. Following a decade of falling interest rates, they believe we could be approaching the point of “regime change.” Central bankers have started to rein in and taper their asset purchases and have begun raising interest rates to offset inflationary pressures. This turn in the direction of monetary policy has implications for all asset classes. Much of the “buy case” for equities has rested on their offer of relative value compared to low-yielding bonds. For a while, equities have not looked cheap in absolute terms. The view of MFS is that equity valuations in some sectors look stretched and risks abound – including heightened inflation, fading stimulus, higher taxes, trade wars, potential central bank policy mistakes, new COVID variants, and ongoing worldwide geopolitical risks. MFS believes that rising inflation and interest rates could cause a setback in the markets at some point. While predicting outcomes is impossible, their view is that equity returns in the coming decade could be lower than they have been over the past one.

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57

GROWTH OF $10,000 INVESTMENT - CLASS II

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

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What is the investment approach of MML Large Cap Growth Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital appreciation by investing primarily in large-capitalization companies that the Fund’s subadviser believes offer the potential for long-term growth. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in the common stocks of companies whose market capitalizations at the time of purchase are within the market capitalization range of companies included in the Russell 1000^® Growth Index. The Fund’s subadviser is Loomis, Sayles & Company, L.P. (Loomis Sayles).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 18.41%, significantly underperforming the 27.60% 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.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Review, beginning on page 3.

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

For the year ended December 31, 2021, the Fund’s stock selection in the consumer discretionary, health care, consumer staples, communication services, information technology, energy, and financial sectors – as well as the Fund’s allocations to the information technology, industrials, health care, consumer staples, and financial sectors – detracted from relative performance.

With respect to specific Fund holdings, Alibaba and Walt Disney were the biggest detractors from the Fund’s full-year performance. A Fund holding since its initial public offering (IPO) in the third quarter of 2014, Alibaba is a leading China e-commerce and consumer-engagement platform provider. Its shares have been under pressure since late 2020, due to investor concerns regarding increasing regulatory intervention by the Chinese government. The Fund trimmed its position in Alibaba and reallocated the proceeds to its existing holdings in Boeing, Disney, Illumina, and Salesforce. Founded almost 100 years ago, Disney is one of the largest and most renowned vertically integrated media companies in the world. The entertainment conglomerate boasts iconic, revered entertainment brands and decades of film and TV content that it leverages across its media networks, theme parks, motion picture studios, and direct-to-consumer businesses. During 2021, Disney reported financial results that continued to be significantly impacted by COVID-19, but were largely in line with, or better than, consensus expectations for revenues and profitability.

On the other side of the ledger, stock selection in the industrial sector, as well as the Fund’s allocations to the energy, communication services, and consumer discretionary sectors, contributed positively to relative returns. Nvidia and Alphabet were the two top contributing Fund holdings for the year. Nvidia is the world leader in graphic processing units (GPUs), which enable computers to produce and utilize highly realistic 3D graphic imagery and models. The company reported financial results during the reporting period that were better than consensus expectations, driven by broad-based strength that included quarterly revenue records in the company’s gaming, data center, and professional visualization segments. Alphabet (the parent company of Google) is a holding company that owns a collection of businesses – the largest and most important of which is Google. Google is the global leader in online search and advertising, and also offers online cloud solutions to businesses and consumers globally. A long-term portfolio holding, Alphabet reported financial results during the period that reflected a strong recovery in advertising spending, which had been depressed due to COVID-19, while revenue growth accelerated and adjusted operating margins expanded. The company’s search and YouTube businesses both benefited from strong growth in direct response ads, and YouTube further benefited from strong demand from brand advertisers due to its reach and engagement with over 2 billion monthly users who recently spent over 1 billion hours daily on the platform.

Subadviser outlook

The Fund’s investment process is characterized by bottom-up, fundamental research and a long-term investment time horizon. The nature of Fund management’s process is designed to lead to a lower turnover portfolio, where sector positioning is the result of stock selection. At year end, the Fund was overweight in the health care, communication services, industrial, energy, financial, and consumer staples sectors – and underweight in the information technology and consumer discretionary sectors. The Fund did not have exposure to stocks in the real estate, materials, or utilities sectors. Fund management remains committed to its long-term investment approach to invest in those few high-quality businesses with sustainable competitive advantages and profitable growth when they trade at a significant discount to intrinsic value.

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60

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

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What is the investment approach of MML Managed Volatility Fund and who is the Fund’s subadviser?

The Fund seeks to capture the majority of the returns associated with equity market investments, while exposing investors to less risk than other equity investments. Under normal circumstances, the Fund invests in a broadly diversified portfolio of common stocks, while also selling index call options and purchasing index put options. The Fund’s stock portfolio will have approximately 500 stocks, and seeks to duplicate the investment composition and return of the S&P 500^® Index* (the “Index”) by holding each stock included in the Index in approximately the same proportion as each stock’s relative weighting in the Index. The Fund’s subadviser is Gateway Investment Advisers, LLC (Gateway).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 11.54%, significantly underperforming the 28.71% return of the Index, which measures the performance of 500 widely held stocks in the U.S. equity market. The Index is the Fund’s benchmark. The Fund outperformed, by a wide margin, the -1.54% return of the Bloomberg U.S. Aggregate Bond Index, 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).

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

The Fund underperformed its primary benchmark for the year, while achieving the risk component of its objective by exhibiting significantly less risk than the equity market. Returns for the year were aided by relatively elevated implied volatility. Throughout 2021, the Fund’s two-part option strategy delivered equity market participation during the periods in which the equity market advanced and significant downside protection during market declines. Specifically, the Fund had smaller losses than the Index when equity market returns were negative in January and September, and provided 2.39% of risk mitigation with a return of -2.73% during the maximum drawdown period for the Index from September 2 through October 4.

The Fund’s positive but lagging returns of 3.29%, 3.92% and 4.44% in the first, second, and fourth quarters, respectively, of 2021, led to its underperformance for the year, as the Fund was unable to keep pace with the Index’s strong advances. When the equity market advances at an above-average rate, underperformance is expected, as the risk-reducing option strategy generates losses that detract from returns. Consequently, the fourth quarter, the strongest equity market quarter of the year, produced the most significant period of lagging performance for the Fund.

From October 4 through November 18, as the equity market’s recovery from its drawdown developed into a rally to new highs, the Fund generated a return of 3.80%, while the Index advanced 9.60%. Over the remainder of the year, the Index added 1.47% to its return, while the Fund returned 0.69%.

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. While the Fund’s options strategy did provide some downside protection throughout the year, performance was not significantly impacted by the Fund’s use of put and call options. (A put option is an agreement that gives the owner the ability to sell a specified amount of an underlying security at a specified price within a specified period of time. A call option is an agreement that gives the owner the ability to buy a specified amount of an underlying security at a specified price within a specified period of time.)

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Subadviser outlook

Fund management’s investment philosophy is informed by its long history and maintains that the equity market is the most reliable source of attractive long-term returns, despite its high volatility relative to other asset classes and tendency to periodically deliver significant short-term losses. Their investment philosophy also holds that consistency is key to long-term success and that generating cash flow with index options, rather than seeking to forecast the market, can be a lower-risk means to participate in equity markets. By staying true to this philosophy and continuing to manage strategies consistent with the firm’s historical approach, Fund management seeks to manage risk while pursuing long-term returns in an uncertain environment.

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64

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

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What is the investment approach of MML Mid Cap Growth Fund, and who are the Fund’s subadvisers?

The Fund seeks long-term capital appreciation by investing primarily in equity securities of mid-capitalization companies that the Fund’s subadvisers believe offer the potential for above-average earnings growth. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in a broadly diversified portfolio of common stocks of mid-cap companies whose earnings the Fund’s subadvisers expect to grow at a faster rate than the average company. The Fund’s two subadvisers are T. Rowe Price Associates, Inc. (T. Rowe Price), which managed approximately 75% of the Fund’s portfolio; and Wellington Management Company LLP (Wellington Management), which managed approximately 25% of the Fund’s portfolio, as of December 31, 2021.

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 13.21%, outperforming the 12.73% return of the Russell Midcap^® Growth Index (the “benchmark”), which measures the performance of the mid-cap growth segment of the U.S. equity universe. It includes Russell Midcap Index companies with higher price-to-book ratios and higher forecasted growth values. The Fund’s 13.21% return significantly underperformed the 24.76% return of the S&P MidCap 400^® Index, which measures the performance of mid-sized U.S. companies, reflecting the distinctive risk and return characteristics of this market segment. It comprises stocks in the middle capitalization range, covering approximately 7% of the of U.S. equity market.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, within the T. Rowe Price component of the Fund, broadly speaking, stock selection and sector allocation contributed to the Fund component’s relative results. At the sector level, communication services, consumer discretionary, and materials aided relative returns; the health care and industrial and business services sectors detracted. The communication services sector was the largest contributor to relative performance, due to stock selection and an underweight allocation to the sector, relative to the benchmark. Shares of Fund component holding Liberty Media Formula One Corp, which controls the exclusive commercialization of the immensely popular F1 motorsport races, gained ground, as COVID-19 vaccinations enabled the return of in-person sporting events. Fund component holdings in the materials sector also aided relative returns, although that was partially offset by an overweight exposure to the sector. Fund component holding Sealed Air Corporation, a packaging solutions company specializing in food and product protection, saw its shares surge on the back of strong earnings and its ability to exceed expectations around managing inflation risk. In contrast, Fund component holdings in the health care sector detracted from performance, driven by Teleflex. Shares of the medical supply company had been volatile since the spring of 2021, when a resurgence of coronavirus cases prompted fears that elective and noncritical medical visits and procedures would be cancelled or postponed, curtailing demand for the company’s products. Clarivate (a public analytics company that operates a collection of bibliometric subscription-based services) is a Fund component holding in the industrial and business services sector. Its shares declined for various reasons, including a deceleration in subscription growth, investor concerns regarding an acquisition, and a secondary share offering. 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 estimated impact from employing warrants was negligible during the reporting period.

With respect to the Wellington Management Fund component, strong stock selection within the communication services sector was a primary driver of relative performance, which was slightly offset by weak stock selection in the information technology and industrial sectors. Sector allocation, a residual of Wellington Management’s bottom-up stock selection process, also weighed on relative returns. An overweight to the financial sector contributed to relative performance, while an overweight to the communication services sector and a lack of exposure to real estate detracted. Fund component holdings that were top individual contributors to relative performance included CDW (tech hardware) and KLA (semiconductor equipment). CDW is a provider of technology products and services to small and mid-sized enterprises, governments, and schools. Its share price rose after the company reported strong fourth-quarter 2021 results coming in ahead of consensus on the top and bottom lines. KLA, a U.S.-based supplier of process control and yield management solutions for the semiconductor industry, revised its

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expectations higher for 2021 wafer fab equipment spending, with the view that 2022 would mark another year of growth for the industry. Fund component holdings that detracted the most from relative returns included Chegg (consumer services) and Shift4 Payments (software). Chegg is an online education platform that offers students tools and resources to help with their studies. The company reported weak results, sending the stock down on much lower-than-expected guidance as management highlighted weak enrollment trends and subscriber growth, with limited visibility into when this would turn around. Shift4 Payments, a payment processor that provides software-enabled payment services with a particular expertise in the restaurant and lodging verticals, also detracted from relative results. Its share price fell in the third quarter of 2021, despite announcing solid quarterly results and increased fiscal year 2021 guidance.

Subadviser outlook

T. Rowe Price notes that, while there are signs that a correction may have begun in the most expensive, growth-at-any-price stocks, they believe that the correction could still be in the early innings and that it may not proceed in a straight line. T. Rowe Price believes that global markets face more uncertain prospects in 2022, noting that higher inflation, a shift toward monetary tightening, and new coronavirus variants all pose potential challenges for economic growth and earnings. Regardless of the environment, T. Rowe Price’s focus remains on owning quality companies with durable growth prospects and prudent balance sheets.

At the end of the year, the Wellington Management Fund component had its largest overweight allocation to the communication services and health care sectors, and its greatest underweight positions in the real estate, consumer discretionary, and materials sectors. Wellington Management believes the Fund component is well-positioned for a stable growth environment looking ahead, and they believe in the potential of the quality of the holdings in the portfolio and their ability to generate outperformance over the long term.

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68

GROWTH OF $10,000 INVESTMENT - INITIAL 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.

* Benchmark

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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

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What is the investment approach of MML Mid Cap Value Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital growth. Income is a secondary objective. The Fund invests primarily in equity securities of mid-capitalization companies that the Fund’s subadviser believes offer prospects for long-term capital growth. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of medium-size companies. The Fund’s subadviser is American Century Investment Management, Inc. (American Century).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 23.31%, significantly underperforming the 28.34% return of Russell Midcap^® Value Index (the “benchmark”), which measures the performance of the mid-cap value segment of the U.S. equity universe. It includes Russell Midcap Index companies with lower price-to-book ratios and lower forecasted growth values.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

For the year ended December 31, 2021, stock selection in the materials sector detracted from the Fund’s relative performance. In particular, some of the Fund’s higher-quality holdings in the containers and packaging industry hampered results. Stock selection in the financial sector also hindered performance, including not owning a number of companies from the banking industry. On a positive note, stock selection in the industrial sector benefited performance. Stock selection in the energy sector – particularly, the oil, gas and consumable fuels industry – also supported the Fund’s returns.

With respect to specific Fund holdings, key detractors during the year included Zimmer Biomet Holdings and Pinnacle West Capital. Medical device company Zimmer Biomet Holdings underperformed, following strong returns in the second half of 2020, when elective surgeries began to be allowed during the pandemic. With the omicron COVID-19 surge toward the end of 2021, however, elective surgeries have once again been delayed by many providers. Arizona-based utility Pinnacle West Capital also underperformed, due to regulatory overhangs surrounding its pending general rate case in Arizona. Although the Arizona Corporation Commission delivered a disappointing final determination on the case in early November, the stock rallied at the end of the year.

Fund holdings that were key contributors to performance during the year included ConocoPhillips and nVent Electric. ConocoPhillips, an exploration and production company, outperformed after the company announced an acquisition that the market viewed as attractively priced. In addition, high commodity prices raised the free cash flow and return on invested capital generation potential of the business. nVent Electric, a provider of electrical products, recently delivered strong quarterly results, which increased its share price.

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 currency forwards to hedge non-U.S. exposure. The use of derivatives did not have a material impact on performance.

Subadviser outlook

Fund management notes that easy monetary policy and generous fiscal spending have buoyed the market since mid-2020. Confident investors have been willing to take on risks, including bidding up the prices of lower-quality companies at the greatest risk from an economic downturn. Fund management believes that this behavior has created an opportunity for investors who focus on overlooked higher-quality businesses. In the months ahead, their view is that investors will assess risk more prudently as stimulus fades, economic growth moderates, and interest rates and inflation rise. Based on their analysis, Fund management believes that this creates an opening for quality-focused investors because certain high-quality stocks are now trading at a large discount to low-quality stocks.

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71

GROWTH OF $10,000 INVESTMENT - INITIAL 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 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. The Fund’s return reflects changes in the net asset value per share without the deduction of any product charges (e.g., cost of insurance, mortality and expense risk charges, administrative fees, and CDSL). The inclusion of these charges would have reduced the performance shown here.

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What is the investment approach of MML Small Cap Growth Equity Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital appreciation by investing primarily in equity securities of smaller companies that the Fund’s subadviser believes offer potential for long-term growth. Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in the equity securities of companies whose market capitalizations at the time of purchase are within the market capitalization range of companies included in the Russell 2000^® Index or the S&P SmallCap 600 Index. The Fund’s subadviser is Wellington Management Company LLP (Wellington Management).

How did the Fund perform during the 12 months ended December 31, 2021?

The Fund’s Initial Class shares returned 7.31%, outperforming the 2.83% return of the Russell 2000 Growth Index (the “benchmark”), which measures the performance of the small- to mid-cap growth segment of the U.S. equity universe. It includes Russell 2000 Index companies with higher price-to-book ratios and higher forecasted growth values. The Fund’s 7.31% return underperformed the 14.82% return of the Russell 2000 Index, 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 December 31, 2021, please see the Economic and Market Overview, beginning on page 3.

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

Sector allocation, a residual of the Fund’s bottom-up stock selection process, aided relative returns for the year ended December 31, 2021. The Fund’s overweight allocations (relative to the benchmark) to the information technology and consumer discretionary sectors, and its underweight allocation to the health care sector contributed to performance. Conversely, security selection was a detractor, as the Fund’s less-than-favorable stock selection in the health care and financial sectors was only partially offset by stronger stock choices in the information technology and industrial sectors.

With respect to specific Fund holdings, top individual contributors to relative performance during the period included Perficient (information technology) and Skyline Champion (consumer discretionary). Perficient was both the top relative and absolute contributor. Shares of Perficient, a digital consultancy firm, rose after posting strong second-quarter 2021 results at the end of July. Revenues beat consensus estimates, with earnings per share (EPS) also coming in higher than expected. Shares of Skyline Champion increased after the company reported second-quarter 2021 earnings that exceeded expectations, driven by greater net sales. The U.S.-based homebuilder saw an increase in an already strong backlog, as it remained focused on increasing production amid the rising supply chain challenges.

Fund holdings that were top relative detractors from performance included Haemonetics (health care) and Ollie’s Bargain Outlet (consumer discretionary). Haemonetics was both the top relative and absolute detractor. During the reporting period, shares of Haemonetics fell on the announcement that CSL Plasma, one of its largest customers, would not be renewing its supply agreement with the medical technology company for the use of plasma collection system devices. Shares of Ollie’s Bargain Outlet fell, as investors reacted negatively to the discount retailer’s second-quarter earnings report. Results were weak against 2020’s record results, when the company benefited from the initial COVID-19 retail backdrop by keeping its stores open. Additionally, Ollie’s cut its margin forecast for full-year 2021, citing significantly higher supply chain costs in the second half.

Subadviser outlook

Fund management notes that volatility within the small-cap universe has remained elevated, driven by macroeconomic factors, including rising inflation and interest rates, gradual tightening of monetary and fiscal policy, and the pace of economic recovery. Further, the discovery and subsequent rapid spread of the highly transmissible COVID-19 omicron variant created additional uncertainty related to the trajectory of the pandemic and reopening timelines. Fund management anticipates these factors could have a strong impact on investor sentiment during 2022. At the end of the year, the Fund held its largest overweight allocations to the industrial and consumer staples sectors and its most underweight allocations to the health care and information technology sectors.

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GROWTH OF $10,000 INVESTMENT - INITIAL 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.