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

“At MassMutual, our goal is to help you build the future you want for yourself and your family. We want to help you with your retirement plans today, so you can feel more comfortable about tomorrow.”

December 31, 2022

Continued market volatility challenges retirement investors

I am pleased to present you with the MML Series Investment Fund Annual Report. During the fiscal year ended December 31, 2022, U.S. stocks were down over 18%, with many investors concerned about the likelihood of a recession, as the U.S. Federal Reserve Board (the “Fed”) aggressively tightened monetary policy to combat heightened inflation. Stocks in foreign developed markets and emerging markets also experienced significant losses in the fiscal year, hurt by elevated energy prices, a strengthening U.S. dollar, and concerns that consumer spending and corporate earnings growth would slow. U.S. bond investors experienced negative returns in the rising interest rate environment, fueled by aggressive interest rate hikes by the Fed that were aimed at reducing demand-driven inflationary pressures.

Suggestions for retirement investors under any market conditions

¹ 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.

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Is this a good 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:

Get to where you want to be

At MassMutual, our goal is to help you build the future you want for yourself and your family. We want to help you with your retirement plans today, so you can feel more comfortable about tomorrow. That’s why we continue to encourage you to maintain perspective when it comes to retirement investing, regardless of any headline-making events. MassMutual’s view is that changing market conditions have the potential to reward patient investors. Thank you for your continued confidence and trust in MassMutual.

Sincerely,

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

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

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

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

MM202401-303982

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Continued market volatility challenges retirement investors

During the fiscal year ended December 31, 2022, U.S. stocks were down over 18%, with many investors concerned about the likelihood of a recession, as the U.S. Federal Reserve Board (the “Fed”) aggressively tightened monetary policy to combat heightened inflation. Stocks in foreign developed markets and emerging markets also experienced significant losses in the fiscal year, hurt by elevated energy prices, the strengthening U.S. dollar, and concerns that consumer spending and corporate earnings growth would slow. U.S. bond investors experienced negative returns in the rising interest rate environment, fueled by aggressive interest rate hikes by the Fed that were aimed at reducing demand-driven inflationary pressures.

Market Highlights

Market Environment

For the fiscal year beginning on January 1, 2022, global stock investors experienced significant losses. U.S. stocks fell sharply in the period in response, with the S&P 500 Index^®* (“S&P 500”) entering bear market territory after declining more than 20% from its previous highs. Investors sought safety from high inflation, rising interest rates, and the increasing possibility of a recession. Consumer sentiment fell sharply, down 15.7% in the period¹, as high inflation – driven by rising energy, food, and housing costs – overwhelmed low unemployment and strong wage growth. As of November 2022, consumer loan levels were at record highs, having increased by 11.8% year-over-year², as more Americans are borrowing to make ends meet in these inflationary times.

* 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.

¹ University of Michigan: Consumer Sentiment (UMCSENT), retrieved from FRED, Federal Reserve Bank of St. Louis;
https://fred.stlouisfed.org/series/UMCSENT, December 23, 2022.

² Board of Governors of the Federal Reserve System (US), Consumer Loans, All Commercial Banks [CONSUMER], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/CONSUMER, December 30, 2022.

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As a result, the broad market S&P 500 fell 18.11% for the period. The technology-heavy NASDAQ Composite Index performed even worse, dropping 32.54%. The more economically sensitive Dow Jones Industrial Average^SM was down 6.86%. During the reporting period, small-cap stocks underperformed their larger-cap peers, while value stocks outperformed their growth brethren. The communication services, consumer discretionary, information technology, and real estate sectors were all down by 25% or more for the period. The energy sector was the strongest performer for the fiscal year, up 65.72%, aided by a 6.6% increase in the price of West Texas Intermediate (WTI) crude oil. The utilities sector also ended the period positively, gaining 1.57% for the period.

Developed international markets, as measured by the MSCI EAFE^® Index, generally outperformed their domestic peers, ending the fiscal year down 14.45%. Emerging-market stocks, as measured by the MSCI Emerging Markets Index, also fell sharply, ending down 20.09% for the period. Investors sold off developed international and emerging-market stocks on concerns that higher interest rates and commodity prices would impair consumer spending and corporate earnings growth.

Bond yields rose sharply during the fiscal year, with the 10-year U.S. Treasury bond yield rising from a low of 1.63% on January 1, 2022 to close the period at 3.88%. Rising yields generally produce falling bond prices; consequently, bond index returns suffered. The Bloomberg U.S. Aggregate Bond Index ended the period down 13.01%. Investment-grade corporate bonds fared even worse. The Bloomberg U.S. Corporate Bond Index, which tracks investment-grade corporate bonds, ended the period with a 15.76% loss. The Bloomberg U.S. Corporate High-Yield Bond Index also ended in negative territory, declining 11.19% for the period.

Review and maintain your strategy

MassMutual is committed to putting our clients’ needs first. We use our innovative open-architecture platform to craft solutions that can help deliver in all stages of the investor’s journey. From building potential wealth to retiring comfortably, we work continually to help investors secure their futures and protect the ones they love. While the current market volatility, including the reality of market sell-offs, can test an investor’s mettle, we’d like to remind you that, as a retirement investor, it’s important to maintain perspective and have realistic expectations about the future performance of your investment accounts. As described in this report, financial markets can reverse suddenly with little or no notice. That’s why we continue to believe that retirement investors should create and maintain a plan that focuses on their goals, how long they have to invest, and how comfortable they are with market volatility. Our multi-managed and sub-advised mutual funds tap into the deep expertise of seasoned asset managers who are committed to helping long-term investors prepare for retirement – in all market conditions. As always, we recommend that you work with a personal financial professional, who can help you define an investment strategy that aligns with your comfort level with respect to market volatility, how long you have to save and invest, and your specific financial goals. Thank you for your confidence in MassMutual.

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

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

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

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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, 2022?

* Benchmark return

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Each of the MML Allocation Series Funds outperformed its respective Custom Index, the Russell 3000 Index, and the MSCI ACWI ex USA Index. All five Funds underperformed 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, 2022, 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, 2022, the Series Funds delivered negative returns, as stocks underperformed fixed-income investments in 2022. Consequently, those Series Funds with higher equity allocations underperformed their Series Funds counterparts with higher fixed-income allocations.

For the fiscal year ended December 31, 2022, global stock investors experienced significant losses. During that time, investors sought safety from high inflation, rising interest rates, and the increasing possibility of a recession. As a result, the broad market S&P 500 Index^® fell 18.11% for the period. The technology-heavy NASDAQ Composite Index performed even worse, dropping 32.54% for the period. The more economically sensitive Dow Jones Industrial Average^SM was down 6.86% for the period.

During the reporting period, small-cap stocks underperformed their larger-cap peers, while value stocks outperformed their growth brethren. Developed international markets outperformed their domestic peers, ending the fiscal year down 14.45% as measured by the MSCI EAFE^® Index. Emerging-market stocks, as measured by the MSCI Emerging Markets Index, also fell sharply, ending down 20.09% for the period. Some investors sold off developed international and emerging-market stocks on concerns that higher interest rates and commodity prices would impair consumer spending and corporate earnings growth.

Bond yields rose sharply during the fiscal year, with the 10-year U.S. Treasury bond yield rising from a low of 1.63% on January 1, 2022 to close the period at 3.88%. Rising yields generally produce falling bond prices; consequently, bond index returns suffered. The Bloomberg U.S. Aggregate Bond Index ended the period down 13.01%. Investment-grade corporate bonds fared

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even worse. The Bloomberg U.S. Corporate Bond Index, which tracks investment-grade corporate bonds, ended the period with a 15.76% loss. The Bloomberg U.S. Corporate High-Yield Bond Index also ended in negative territory, declining 11.19% over the period.

Manager selection contributed to overall performance in 2022. Strong performance by the MML Income and Growth, MML Equity and Income, MML Fundamental Value, MML Focused Equity, and MML Mid Cap Value Funds helped overall performance. Weak performance by the MML Blue Chip Growth, MML Small/Mid Cap Value, MML Foreign, MML Strategic Emerging Markets, MML Managed Bond, MML Total Return Bond, and MML Inflation-Protection and Income Funds were significant drivers of underperformance.

Investment adviser outlook

Despite the stock market sell-off in 2022, we view the stock markets as extended and valuations high relative to market history. In MML Advisers’ view, while the prospect of positive economic and corporate earnings growth supports a bull case, MML Advisers believes that more clarity on the slowing of economic growth, persistency of inflation, labor costs, China’s COVID-19 policy, and the impact of monetary policy tightening is needed for the allocation to stocks to increase. Against this backdrop, we believe that diversification across global assets for investors could be a sensible approach for what, in our view, could be a bumpy economic ride.

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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.

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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 235 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, 2022?

The Fund returned -30.29%, significantly underperforming the -18.11% 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 underperformed the -29.14% 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, 2022, 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 had its worst year since 2008 during the one-year period ended December 31, 2022, as persistently high inflation and aggressive rate hikes stoked recessionary fears. In 2022, the benchmark entered its first bear market since 2020. Energy was the top S&P 500 sector for the second straight year, climbing 66% for the one-year period ended December 31, 2022. Crude oil prices spiked in March 2022 after Russia’s invasion of Ukraine upended global oil flows.

Growth stocks had the sharpest declines during the reporting period, including several technology giants that had been market leaders over the last decade. Despite consecutive quarters of negative gross domestic product (GDP) growth in the first half of 2022, a strong labor market helped inflation to persist throughout the reporting period.

With respect to the Fund’s performance, stock selection within the materials sector was the top contributor to relative returns. The Fund’s position in energy industry firm Halliburton buoyed results, as its stock outpaced the broader industry. On the downside, Fund holdings within the communication services sector weighed on results. From a Fund holdings perspective, Tesla was the top individual detractor from returns for the reporting period.

Capital Research’s outlook

In Fund management’s view, the overall uncertain economic environment and challenges of inflation are very real concerns. Fund management believes the Fund may be well positioned for the road ahead as they continue to focus on capital appreciation and selecting companies best suited for what Fund management expects to be a challenging economic environment in 2023. Fund management remains confident their time-tested investment approach, based on thorough research and robust debate with an eye on valuation, has the potential to continue to deliver favorable outcomes for investors over the long term.

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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 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” that 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, 2022?

The Fund returned -13.70%, outperforming the -18.11% 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 the -16.00% 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 underperformed the -13.01% 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 -13.70% return outperformed the -15.93% 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, 2022, 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 component-specific discussions focus on results 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 one-year period ended December 31, 2022, as U.S. fixed income markets fell across the board. During the reporting period, the largest contributions to relative results came from duration positioning and agency MBS. The Bond Fund’s lower-than-benchmark duration helped reduce interest rate sensitivity as rates moved higher and bond prices fell over the period. A lower position in MBS also helped, relative to the benchmark, as spreads widened materially. On the downside, yield curve positioning and a modest position in emerging markets and high-yield bonds detracted from results. 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 reporting period, the Bond Fund used derivatives as tools for implementing the portfolio’s duration, curve, and credit. Collectively, the use of derivatives detracted from the Bond Fund’s results.

The American Funds Insurance Series – Washington Mutual Investors Fund (the “Income and Growth Fund”) significantly outperformed the benchmark for the one-year period ended December 31, 2022, as U.S. equities had their worst year since 2008. Income and Growth Fund holdings in the consumer discretionary and information technology sectors were additive to relative returns. Among individual securities, the Income and Growth Fund’s higher-than-benchmark position in health care insurer

17

UnitedHealth Group was a top contributor, as the stock outpaced the broader market. On the downside, security selections within the financial and real estate sectors were top detractors. A lower-than-benchmark position in ExxonMobil weighed on relative returns, as that Fund holding stock outpaced the market overall.

The American Funds Insurance Series – Growth-Income Fund (the “Growth-Income Fund”) outperformed the benchmark for the one-year period ended December 31, 2022, in an environment where persistently high inflation and aggressive rate hikes stoked recessionary fears. During the reporting period, the Growth-Income Fund’s investments in the information technology and industrial sectors were top contributors to relative returns. An out-of-benchmark position in energy company Canadian Natural Resources was a top individual contributor, as that Fund holding outpaced the market overall. On the downside, security selections within the communications and financial sectors dragged on returns. Netflix was the Growth-Income Fund’s top individual detractor, owing to a larger-than-benchmark position and returns that lagged the market.

The American Funds Insurance Series – International Fund (the “International Fund”) underperformed the MSCI ACWI ex USA (the “Index”) for the one-year period ended December 31, 2022, as global stocks fell sharply – pressured by rising interest rates, slowing economic growth, and inflationary pressures not seen since the 1980s. Stock selection within the information technology sector dragged on returns. With respect to specific International Fund holdings, a larger-than-Index position in South Korean chipmaker SK Hynix was among the top individual detractors. Turning to the positive, stock selection within the energy sector boosted relative returns. Specifically, the International Fund’s higher-than-benchmark position in Petroleo Brasileiro, a state-owned Brazilian multinational petroleum provider, was a top contributor, as the stock significantly outpaced the broader market.

Investment adviser outlook

Despite the stock market sell-off in 2022, MML Advisers views the stock markets as extended and valuations high relative to market history. In MML Advisers’ view, while the prospect of positive economic and corporate earnings growth seems to support a bull case, MML Advisers believes that more clarity on the slowing of economic growth, persistency of inflation, labor costs, China’s COVID-19 policy, and the impact of monetary policy tightening is needed for the allocation to stocks to increase. Against this backdrop, MML Advisers believes that diversification across global assets for investors for the Fund could be a sensible approach for what, in MML Advisers’ view, could be a bumpy economic ride.

18

19

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.

20

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 is non-diversified, which means that it may hold larger positions in a smaller number of issuers than a diversified fund. 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, 2022?

The Fund’s Initial Class shares returned -39.50%, significantly underperforming the -29.14% 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 significantly underperformed the -18.11% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

Overall, for the one-year period ended December 31, 2022, stock selection and sector allocation detracted from the Fund’s relative performance. The communication services, consumer discretionary, and information technology sectors were the key drivers of the Fund’s underperformance, while the health care and financial sectors were the largest contributors.

Communication services was the largest relative underperformer, due to the Fund’s overweight allocation to the sector, relative to the benchmark, and stock selection within the sector throughout the period. For example, during the period, shares of Fund holding Meta sold off sharply, due in part to headwinds from Apple iOS privacy changes and a significant drop in advertising demand, with macro headwinds putting downward pressure on advertiser budgets. The consumer discretionary sector also detracted from the Fund’s performance on a relative basis due to unfavorable stock choices such Fund holding Carvana, a used car retailer. During the period, shares of this Fund holding traded lower, amid a challenging backdrop that included supply constraints, affordability concerns for consumers (in an environment of rising used car prices and higher financing rates), and concerns around the company’s liquidity runway. Fund holdings in the information technology sector further hampered the Fund’s relative results.

In contrast, health care contributed the most to the Fund’s relative performance during the period, due to beneficial security selection within, and an overweight allocation to, the sector. Shares of Fund holding UnitedHealth Group held up relatively well due to better-than-expected cost trends, as utilization returned to normal and stronger-than-expected onboarding of value-based care patients within Optum (which delivers care aided by technology and data). UnitedHealth Group also benefited from innate defensive characteristics that provided additional support as markets continued to skid lower. The financial sector also bolstered the Fund’s relative returns during the period, driven by favorable security selection and the Fund’s overweight allocation to the sector.

Subadviser outlook

Heading into 2023, in Fund management’s view, capital markets appeared to have priced in a significant global economic slowdown. In Fund management’s view, the key question is whether this deceleration will end in a “soft landing” – with slower, but still positive, growth – or in a full-fledged recession that drags down earnings. T. Rowe Price believes that much depends on the U.S. Federal Reserve and the world’s other major central banks, as they continue efforts to bring inflation under control by hiking interest rates and draining liquidity from the markets. Nevertheless, Fund management’s view is that geopolitical risks could remain potential triggers for downside volatility in 2023. Structural factors, such as bank capital requirements that constrain market liquidity, could magnify price movements, both up and down. Fund management’s view is that although there are good reasons for caution in 2023, excessive pessimism and volatility could create value for agile investors.

21

22

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.

23

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, 2022?

The Fund’s Initial Class shares returned -3.57%, outperforming the -7.54% 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, 2022, please see the Economic and Market Review, beginning on page 3.

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

For the one-year period ended December 31, 2022, favorable security selection and sector allocation drove relative the Fund’s outperformance relative to the benchmark. During the period, the financial, health care, and consumer discretionary sectors were significant relative contributors, while the energy, industrial, and business services sectors were notable detractors.

The financial sector was the primary relative contributor for the period, due to strong stock selection. Fund holding American International Group outperformed the benchmark over the period. Its shares benefited from a strong property and casualty pricing cycle that allowed the company to focus on pushing price, in addition to improved underwriting. Fund holdings in the health care sector also aided relative performance during this time. Shares of pharmaceutical company AbbVie outperformed the health care sector over the period. Shares advanced in April 2022 after the Food and Drug Administration approved RINVOQ and SKYRIZI^® for use. T. Rowe Price believes that this may help balance sales deficits from Humira’s patent loss in 2023. The consumer discretionary sector also contributed to relative returns during the period due to positive stock choices, coupled with an underweight allocation to the sector. Shares of Fund holding Las Vegas Sands initially lagged, as China’s increased lockdowns throughout the fiscal year delayed the reopening of the company’s Macau venue. However, Las Vegas Sands’ shares benefited during the third and fourth quarters of 2022, due to a strong recovery in its Singapore operations, which helped offset some of the costs associated with Macau. Additionally, during the fourth quarter of the fiscal year, shares surged following news of Las Vegas Sands and other gaming companies signing 10-year contracts with the Macau government, renewing their casino licenses for the next decade.

On the downside, weak stock selection in the energy sector detracted from the Fund’s relative performance during the period. One Fund holding that detracted over the period was TC Energy. Its shares were lifted early in the year as global natural gas prices dramatically rose following Russia’s invasion of Ukraine. In the third quarter of 2022, however, the company came under pressure, as capital markets risk and a higher interest rate environment weighed on performance. In early December, shares were again pressured, as the company’s Keystone pipeline was shut down following the report of a leak of 14,000 barrels. Finally, Fund holdings in the industrial and business services sectors also hindered the Fund’s relative performance during the period.

Subadviser outlook

In T. Rowe Price’s view, the range of outcomes in the equity market remains abnormally wide as we head into 2023. Fund management expects continued volatility in the markets, as investors react to new metrics as they are reported. Amid such uncertainty, Fund management believes there is risk in being too anchored to a particular macroeconomic outlook. In Fund management’s view, the balance of economic data suggests a recession could be imminent, although such an event is broadly anticipated, making the eventual recession arguably the “most consensus” one in history. T. Rowe Price believes that the severity of the recession will depend on the degree to which the Federal Reserve (the “Fed”) targets the labor market, which remained tight as of the end of the fiscal period, even as economic data weakened. Should the Fed “declare victory” at an inflation level above its stated target, the equity market could rally, in Fund management’s opinion. Conversely, Fund management’s view is that if the Fed’s aim is to disrupt the labor market, the equity market may move lower. In such an uncertain environment, T. Rowe Price believes it is important for the Fund to selectively lean into weakness and trim on strength. Fund management also expects to seek to maintain balance in the Fund’s portfolio, which, in Fund management’s view, could help make the Fund’s performance less dependent on a particular macroeconomic outcome and offer the potential for the Fund to outperform in a variety of markets.

24

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.

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 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, 2022?

The Fund’s Class I shares returned -18.50%, underperforming the -18.11% 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, 2022, 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 one-year period ended December 31, 2022, energy and utilities were the strongest-performing sectors within the Index, returning 65.72% and 1.54%, respectively. The communication services and consumer discretionary sectors exhibited the worst performance across sectors, returning -40.40% and -37.03%, respectively.

In the first quarter of 2022, global equities were dominated by headlines surrounding high inflation and geopolitical unrest, which led to declines across developed and emerging markets. Continued high inflation, compounded by Russia’s invasion of Ukraine, led to a pullback in investor risk appetite. Headwinds for global financial markets continued in the second quarter, with negative returns in most major asset classes outside of cash. Elevated inflationary pressures led to increased investor expectations for monetary policy tightening throughout the quarter, which in turn heightened investor concerns on the economic growth outlook. Despite seeing double-digit gains by mid-August, U.S. equity markets ended with a loss for the third quarter, as investor hopes of a dovish Federal Reserve (the “Fed”) pivot evaporated following hawkish Fed leader rhetoric and more durable core inflation. Interest rates increased sharply in August and September, including a late-September rise stemming from U.K. financial stability concerns. Global markets finished the fourth quarter higher relative to the prior quarters, with investor sentiment buoyed by easing inflationary pressures. However, most major asset classes finished calendar-year 2022 with double-digit losses. Late in the calendar year, declining inflation levels allowed the Fed and European Central Bank to slow the pace of interest rate increases, but at fiscal year-end, a significant amount of uncertainty remained surrounding the future of global interest rates and the duration of restrictive monetary policy.

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 generally 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. There was no impact on the Fund’s performance due to the use of derivatives during the reporting period.

Subadviser outlook

Looking beyond the end of the fiscal period, Fund Management believes 2023 will likely be a turbulent year as inflation and monetary policy fears pivot to a weak global economy, but also to lower inflation and central bank pauses interest rate increases. Fund Management believes pockets of economic durability should limit a U.S. earnings slowdown in the upcoming fiscal year, with potential for sentiment-level upside.

27

28

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.

29

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, 2022?

The Fund’s Class II shares returned -4.69%, significantly outperforming the -19.13% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, strong stock selection drove the Fund’s relative results, particularly within the consumer discretionary, industrial, and financial sectors. This was partially offset by weak stock choices within the health care and materials sectors. Sector allocation, a residual of the Fund’s bottom-up stock selection process, also contributed to relative performance throughout the one-year period. Lack of exposure to communication services, an underweight allocation to information technology, relative to the benchmark, and an overweight allocation, relative to the benchmark, to consumer staples contributed the most. This was partially offset by a lack of exposure to the energy sector and an overweight allocation to the consumer discretionary sector.

With respect to specific Fund holdings, top relative contributors for the period included Northrop Grumman (industrials) and TJX Companies (consumer discretionary). Shares of U.S.-based aerospace and defense company Northrop Grumman rose on strength in the industry, as the conflict in Ukraine led to increased domestic military spending throughout the one-year period. Like its peers, as of the end of the fiscal period, growth was moderating for Northrop Grumman, as the B-21 and F-35 programs plateaued, and the U.S. government was shifting from unmanned aerospace platforms to space platforms, which Fund management expects to take time to play out. Shares of TJX Companies rose over the period due to solid demand, combined with good buying opportunities, as traditional retailers continued to experience inventory challenges. TJX Companies’ management remained focused on future profitability and their long-term goal to be a $60 billion revenue company.

Fund holdings that were among the top relative detractors for the period were Ecolab (materials) and Baxter International (health care). Not owning benchmark constituent ExxonMobil (energy) also proved beneficial for the Fund during the reporting period. Shares of U.S.-based chemical company Ecolab fell when growth stocks traded down during the reporting period after a strong run in 2021. The company grappled with inflation and the impact of supply chain disruptions – logistics and labor costs were also an issue for Ecolab during the course of the period. Baxter International underperformed in 2022 primarily because of continued inflationary pressures due to higher raw material costs, overhead costs, and difficulty securing critical components – specifically chips, due to ongoing chip shortages.

Subadviser outlook

Fund management observed that equity and bond markets both fell precipitously in 2022 over fears around rising interest rates and inflation. The Federal Reserve (the “Fed”) initially held that the early signs of inflation were probably temporary and isolated. However, in Fund management’s view, the eventual realization that inflation was not simply going away forced the Fed (and other central banks) to react late. Significant interest rate bumps chipped away at the foundation of the post-Great Financial Crisis bull market.

At fiscal year-end, in Fund management’s view, the Fund’s principal risk centered on whether the Fed can deftly manage a rate hike journey in 2023 without causing a recession. As of December 31, 2022, the Fund held its largest overweight allocations to the consumer staples and health care sectors, and it was most underweight in the information technology sector.

30

31

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.

32

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, 2022?

The Fund’s Initial Class shares returned -14.58%, underperforming the -14.45% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, on a regional basis, a combination of unfavorable positioning and stock selection within the United Kingdom (“UK”) detracted most from the Fund’s relative returns. The UK was the benchmark’s top-performing region for the year, helped by energy representing the largest sector component. The Fund’s underweight exposure to the select companies in the rallying region and sector, relative to the benchmark, detracted from relative returns. Fund holding Persimmon Plc also weighed on returns. The UK homebuilder sold off after the UK housing secretary announced that developers would be responsible for an estimated £4 billion of cladding remediation; investor concerns over the UK economy also detracted from Persimmon’s returns during the period.

From a sector perspective, consumer discretionary weighed most on relative returns during the period. While the Fund’s underweight allocation to one of the market’s worst-performing sectors was additive, stock selection within the sector hampered results. Shares of Japanese conglomerate Sony Group Corporation detracted most after reporting mixed results over the course of the year. The company’s gaming segment faced higher costs following the Bungie studio acquisition as well as the continued supply shortage of PS5 consoles. However, Sony reported strong results across its other business segments.

Conversely, Europe contributed most to the Fund’s relative results during the period. Stock selection there was on full display, as an array of positions from various industries helped to drive the Fund’s performance. Most notable was Irish financial services company AIB Group PLC, which benefited from a relatively strong local economy and a rising interest rate environment during the one-year period. AIB nearly doubled consensus profit-before-tax expectations in the first half of the year due to an improved net interest margin and a €300 million credit write-back.

From a sector perspective, Fund holdings in the industrial sector contributed most to relative returns during the period. The contribution effects were spread among multiple positions from various industry groups – including aviation, defense, machinery, and conglomerate holdings. French aerospace company Dassault Aviation SA was the top performer among the Fund’s holdings for the fiscal period after the company announced a large military jet order by the Indonesian government in the first quarter of 2022. Shares of the company were further boosted following Russia’s invasion of Ukraine early in the fiscal period, as investors anticipated a rise in European defense spending.

33

Subadviser outlook

Global stock markets mounted a recovery in the final months of 2022, but in TSW’s view, obvious catalysts for further broad-based gains are notably absent as 2023 begins. Fund management believes that central banks may continue to press the case against inflation, the pace of economic expansion could be underwhelming, and nervous caution will be the watchword for consumers and investors. However, TSW believes that, after a few turbulent prior years, global stock valuations appeared reasonable as of the end of the fiscal period. For instance, the MSCI All-Country World ex US Index, a broad measure of developed and emerging market stocks, returned less than 1% per year over the past five years in U.S. dollar terms, suggesting that prices for international stocks reflect low expectations. In Fund management’s view, this could be a good environment for a patient, value-focused investment style, and that returns for active investors over the next five years could be better than recent experience. In TSW’s opinion, TSW’s emphasis on stocks exhibiting attractive value and fundamentally improving operations is well-suited to challenging market conditions like those that TSW expects to exist in the coming fiscal period.

34

35

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.

36

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 Advisers).

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Class II shares returned -20.24%, underperforming the -18.11% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, stock selection within the information technology, financial, and consumer staples sectors was the primary driver of the Fund’s underperformance. This was partially offset by strong stock selection in the communication services sector, a moderate underweight to the consumer discretionary sector, and a moderate overweight to the industrial sector.

Fund holdings that were top detractors from relative performance during the fiscal period included Advanced Micro Devices, Airbnb, and Qualcomm. Advanced Micro Devices, a semiconductor company, saw weakened demand for the company’s consumer central processing unit (CPU) and graphics processing unit (GPU) businesses due to global macroeconomic headwinds. Airbnb, which operates an online marketplace focused on short-term home stays, underperformed, as the stock suffered in an environment that featured a combined sell-off of higher-growth, technology, and travel-related stocks. With respect to travel-related stocks, in Fund management’s view, fears of a weakening economy, in tandem with higher gasoline prices, hurt investor sentiment. Qualcomm – a provider of semiconductors, software, and services related to wireless technology – underperformed, as semi-conductor stocks, and technology stocks more broadly, fell out of favor with investors. The company was also affected by COVID-related headwinds in China, which caused weakness in the handset market that was important to Qualcomm’s growth plans.

Fund holdings that were top contributors to the Fund’s relative performance included two pharmaceuticals companies – Eli Lilly and AstraZeneca – and auto parts retailer, O’Reilly. Eli Lilly reported favorable data for its obesity drug, tirzepatide, and it also received Food and Drug Administration approval to use the drug for type 2 diabetes in adults. During the reporting period, pharmaceutical companies were generally viewed as defensive stocks, which investors favored during the equity sell-off. AstraZeneca reported solid earnings results and modestly raised its dividend during the fiscal period. O’Reilly reported solid earnings and did a significant stock buyback program that was well received during the fiscal period. The company’s business model was also considered relatively defensive, as car repairs are non-discretionary, and many consumers opted to pay for maintenance in lieu of buying a new vehicle in 2022’s generally uncertain economic environment.

Subadviser outlook

In the view of Fund management, as of the end of the fiscal year, the key questions going forward are for how long interest rates must be kept in restrictive territory, and whether the economy can avoid a recession. Fund management believes that the federal funds rate – the Federal Reserve’s overnight bank lending rate – will stay elevated for longer than the market would like, but that a significant recession is unlikely. Nonetheless, as of the close of the fiscal year, Invesco Advisers expected sluggish gross domestic product growth and pressure on corporate profits to last for a year or more. Fund management expects to continue to maintain its discipline around valuation, focusing on companies with competitive advantages and skilled management teams that are out-executing their peers.

37

38

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.

39

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. Although the Fund may invest in companies of any size, the Fund will tend to 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, 2022?

The Fund’s Class II shares returned -4.86%, outperforming the -7.54% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, stock selection and sector allocation both contributed to the Fund’s relative performance. The Fund experienced positive stock selection in the health care, financial, industrial, and consumer discretionary sectors during the fiscal period. In pharmaceuticals and health care, health insurers Cigna and UnitedHealthcare outperformed due to strong earnings and guidance as well as better-than-expected rate increases for government-sponsored insurance. In the financial sector, Fund holding Charles Schwab added value, as rising interest rates resulted in higher net interest income and the company announced a $15 billion share repurchase program. Within the industrial sector, aerospace and defense companies General Dynamics and Howmet outperformed after Russia’s invasion of the Ukraine, and expectations of increased defense budgets globally supported the sector. In consumer discretionary, AutoZone continued to gain market share with commercial customers, resulting in better-than-expected sales and earnings for this Fund holding during the fiscal period. During 2022, the company repurchased about 10% of its outstanding shares. Finally, sector allocation contributed to the Fund’s relative returns due to an overweight allocation to energy and health care, and underweight allocations to real estate and communication services.

Fund holdings within the technology, consumer staples, and communication services sectors detracted during the reporting period. In technology, semiconductor stocks Qualcomm and Micron lagged, as many investors were concerned about future demand in a potentially difficult 2023 economic environment. In consumer staples, consumer goods provider Procter & Gamble detracted, as the company experienced a cost/pricing squeeze during the Fund’s holding period; Fund management consequently eliminated Procter & Gamble from the Fund’s portfolio. Not owning low-growth, defensive food companies such as Archer Daniels-Midland and General Mills also hampered the Fund’s relative performance. In communication services, Alphabet and Meta Platforms underperformed, as online marketing spend slowed relative to expectations. From a sector allocation perspective, the Fund’s overweight allocation to the technology sector and its underweight allocation to utilities and consumer staples reduced relative returns during the fiscal year.

During the reporting period, Fund management increased the Fund’s exposure to the financial and energy sectors and reduced its positions in technology and communication services. In the financial sector, Fund management added to existing holdings, including JP Morgan and Bank of America, as Fund management believed that rising interest rates could help net interest margins and investment income. Within energy, Fund management added to its holdings oil services firm Halliburton, which was achieving strong pricing gains over the course of the fiscal period because of the lack of labor availability for services in the oil patch. In communication services, Fund management sold its position in Meta. The company had looked attractively priced on a historical basis, but Fund management’s expectation of acceleration in online ad revenue late in 2022 failed to materialize.

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 drive stock prices higher. Fund management’s emphasis on bottom-up security selection and sound fundamental analysis historically has led to alpha generation over time. With rising interest rates and an aggressive Federal Reserve determined to fight inflation, as of the end of the fiscal period, Fund management was increasingly concerned about the path of the economy in 2023. Fund management believes that declining inflation expectations are the key for a reversal in sentiment and potential multiple expansion.

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 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’s subadviser normally invests the Fund’s assets across different industries, sectors, countries, and regions, but the Fund’s subadviser may invest a significant percentage of the Fund’s 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, 2022?

The Fund’s Class I shares returned -17.78%, outperforming the -18.14% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

Security selection and an underweight allocation, relative to the benchmark, to both the information technology and consumer discretionary sectors contributed to the Fund’s relative performance for the one-year period ended December 31, 2022. Within the information technology sector, not owning shares of personal electronics maker Apple, software giant Microsoft, and computer graphics processor maker NVIDIA aided the Fund’s relative results. Within the consumer discretionary sector, not owning shares of internet retailer Amazon.com and electric vehicle manufacturer Tesla also strengthened the Fund’s relative results. Elsewhere, not owning shares of social networking service provider Meta Platforms contributed to the Fund’s relative performance. Additionally, overweight allocations to railway operator Canadian Pacific Railway, diversified technology and manufacturing company Honeywell International, and medical devices maker Boston Scientific aided the Fund’s relative returns. The Fund’s underweight position in shares of technology company Alphabet further benefited the Fund’s relative performance.

On the downside, not holding any stocks within the strong-performing energy sector detracted from the Fund’s relative performance for the reporting period. Within the sector, not owning shares of integrated energy companies ExxonMobil and Chevron also hurt the Fund’s relative returns. Stock selection in the health care sector weakened relative results as well. However, there were no individual stocks within this sector, either in the Fund’s portfolio or in the benchmark, that were among the Fund’s largest relative detractors during the fiscal period. Fund holdings in other sectors that dampened relative performance for the fiscal period included overweight positions in cable and broadband companies Liberty Broadband and Comcast, consulting and information technology services provider Accenture, diversified entertainment company Walt Disney, electrical distribution equipment manufacturer Schneider Electric (France), global banking and payments technology provider Fidelity National Information Services, paint and specialty chemicals manufacturer Akzo Nobel (Netherlands), and machinery and industrial products manufacturer Kubota (Japan).

Subadviser outlook

In Fund management’s view, after a year of sharp swings in monetary policy and in the pricing of financial assets, 2023 started off in an environment of continued uncertainty. Fund management believes that central banks are starting to tame inflation; however, in Fund management’s view, there is perhaps a greater risk of policy error as the U.S. and global economies enter the next phase of monetary and fiscal policy moves, with large and continuous changes to interest rates, potentially followed by moderation as inflation starts to fall, offsetting the risk of recession.

After a decade of abundant liquidity, Fund management believes that the new period of quantitative tightening remains largely untested. In their view, the longer-term implications of the new monetary and fiscal regime are still not fully understood. Fund management expects that the volatility in currency markets, in tandem with concerns over military action in Europe (and threatened in Asia), potentially set the stage for volatility in the markets to remain high.

43

44

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.

45

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, 2022?

The Fund’s Initial Class shares returned -0.31%, significantly outperforming the -7.54% 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, 2022, please see the Economic and Market Review, beginning on page 3.

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

For the one-year period ended December 31, 2022, the Fund’s relative performance was strong across the board, as 10 out of 11 sectors contributed positively. Strong stock selection in health care, information technology, and real estate, coupled with the Fund’s underweight allocation to information technology and real estate, added to relative performance. Conversely, consumer discretionary weighed modestly on the Fund’s relative performance, as headwinds from the Fund’s overweight allocation to the sector slightly outpaced positive stock selection.

The Fund benefited from holdings such as energy producer Hess Corporation, where firm commodity prices and increasing production volumes from their asset in Guyana helped propel shares and relative performance higher. During the fiscal period, the industry remained disciplined in adding more supply to the market, which in turn allowed for continued strong cash generation to fund share repurchases and dividend increases. Turning to other Fund holdings, pharmaceutical firm Merck & Co. reported strong results in their pharmaceutical and vaccine franchises during the fiscal year. Throughout the fiscal year, their animal health franchise also posted solid results, and collectively, cash generation was strong and continued to support attractive investments and returns to shareholders via dividends and share repurchases. Other top contributors to the Fund’s relative performance included multinational energy company Phillips 66, health insurer Cigna Corporation, and John Deere – a manufacturer of agricultural machinery, heavy equipment, forestry machinery, diesel engines, drivetrains used in heavy equipment, and lawn care equipment.

On the downside, Stanley Black & Decker, an industrial and tools business, pressured the Fund’s relative performance, as cost headwinds combined with slowing customer demand led company management to lower earnings guidance for this Fund holding. International Flavors & Fragrances, a global supplier of flavors and fragrances, weighed on the Fund’s relative performance, as inventory destocking, combined with volume headwinds, offset favorable pricing and pushed shares lower. Other Fund holdings that were top detractors during the fiscal period included Advance Auto Parts, financial services company Northern Trust, and cable television provider Altice USA, which Fund management eliminated from the Fund’s portfolio in the fourth quarter of 2022.

Subadviser outlook

Fund management believes that the reversal of the value sector’s fortunes over the last 18-24 months appears likely to persist for years to come, as value runs have historically lasted approximately 7 years on average. Despite the sector’s recent success, valuations for value stocks remain, in Fund management’s view, relatively cheap at a 16% discount to market and a 34% discount relative to growth. Historically, forward five-year returns for value at these levels of discount have been meaningfully positive relative to both the market and growth stocks.

In Fund management’s view, the normalization of higher interest rates, in response to inflation (which Fund management believes may remain higher than preferred by central banks), continues to further bolster confidence in Fund management’s view, as of the end of the fiscal period, that value is well-positioned moving into 2023.

46

47

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.

48

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 foreign companies, including companies located in Europe, Latin America, and Asia. 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. 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, as of December 31, 2022.

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Class II shares returned -15.10%, underperforming the -14.45% 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. The Fund underperformed the -14.29% return of the MSCI World Index ex USA, 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, 2022, 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 results in country and sector allocations as a component of the stock selection process. For the one-year period ended December 31, 2022, with respect to country performance relative to the benchmark, country weightings detracted from results, while stock selection contributed. Relative sector performance was negatively impacted by sector weightings, while stock selection contributed to the Fund’s overall results. From a geographic perspective, the Fund component’s exposure to South Korea detracted the most from the Fund’s relative performance – as both underlying holdings lost value during the period – followed by the U.K., where nine of 13 underlying holdings lost value during the period. Mexico and South Korea were the largest negative absolute detractors to the Fund’s performance for the fiscal year. Stock selection in China and Japan contributed positively to the Fund’s relative performance for the fiscal year. Stock selection in India and Denmark were the largest absolute contributors to the Fund’s performance, as a result of the underlying holding in each country gaining value. From a sector perspective, stock selection in financials and a lack of exposure to the energy sector detracted most from the Fund’s relative performance for the fiscal year. In the Fund’s investment in the financial sector, eight of 12 underlying holdings negatively impacted the Fund’s performance. The Fund’s investments in the technology and communication services sector delivered the largest negative returns from a sector perspective and detracted from the Fund’s performance. The industrials and materials sectors generated the best relative performance for 2022, both due to a lower-than-benchmark weighting and positive stock selection. Within the industrial sector, four of the sector’s 15 underlying holdings gained value, led by Sandvik. In materials, five of six underlying holdings gained value, led by Glencore. 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. As of year end, currency hedges contributed slightly to the Fund component’s performance for the year.

For the MFS segment of the Fund, stock selection in the health care sector weighed on relative performance. Within the sector, not owning strong-performing biopharmaceutical company AstraZeneca (United Kingdom) and an overweight allocation, relative to the benchmark, to imaging products and medical-related equipment manufacturer HOYA (Japan) hurt the Fund’s relative results. The Fund component’s underweight allocation to the energy sector also held back relative performance. There, not owning global energy and petrochemicals company Shell (United Kingdom) and integrated energy and petroleum company Total (France) weakened the Fund’s relative results. Security selection and an overweight position in the industrial sector further dampened the Fund’s relative returns, led by overweight allocations to electrical distribution equipment manufacturer Schneider Electric (France), machinery and industrial products manufacturer Kubota (Japan), and air conditioning system manufacturer Daikin Industries (Japan). Fund component holdings that weakened the Fund’s relative returns included semiconductor manufacturer Taiwan Semiconductor Manufacturing (Taiwan), which is not a benchmark constituent, and an overweight position in consulting services provider Capgemini (France). Not owning shares of mining giant BHP Billiton (Australia) also hampered

49

the Fund’s results. Stock selection in the financial sector contributed to the Fund’s relative performance, led by the Fund component’s overweight positions in insurance company AIA Group (Hong Kong), stock exchange Deutsche Boerse (Germany), investment management and banking firm UBS (Switzerland), and insurance provider Zurich Insurance Group (Switzerland). Stock selection in both the consumer discretionary and information technology sectors also supported the Fund’s relative returns. Within the consumer discretionary sector, the Fund component’s overweight position in food catering company Compass Group (United Kingdom) aided relative returns. Within the information technology sector, not owning shares of lithography systems manufacturer for the semiconductor industry ASML (Netherlands) strengthened the Fund’s relative performance. Elsewhere, the Fund component’s overweight allocations to cosmetic products manufacturer Beiersdorf (Germany), pharmaceutical company Novo Nordisk (Denmark), and oil and gas company Galp Energia (Portugal) further bolstered relative returns. 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 the Fund’s relative performance.

Subadviser outlook

While Harris recognizes the challenges facing investors with the current state of financial markets, Harris believes that the lower and more widely dispersed valuations in the market at fiscal year-end allowed Fund management to redeploy capital into increasingly attractive investments. As of the end of the fiscal period, Fund management was optimistic that these decisions have the potential to sow the seeds of future outperformance. Harris remains focused on building a high-conviction Fund portfolio of undervalued businesses that Fund management believes could provide both a margin of safety and the potential for attractive risk-adjusted returns over the long term.

In MFS’s view, after a year of sharp swings in monetary policy and in the pricing of financial assets, MFS observes that 2023 started off in an environment of continued uncertainty. Fund management believes that central banks are starting to tame inflation; however, in Fund management’s view, there is perhaps a greater risk of policy error as the U.S. and global economies enter the next phase of monetary and fiscal policy moves, with large and continuous changes to interest rates, potentially followed by moderation as inflation starts to fall, offsetting the risk of recession. After a decade of abundant liquidity, MFS believes that the new period of quantitative tightening remains largely untested. In their view, the longer-term implications of the new monetary and fiscal regime are still not fully understood. Fund management expects that the volatility in currency markets, in tandem with concerns over military action in Europe (and threatened in Asia), potentially set the stage for volatility in the markets to remain high.

50

51

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.

* 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.

52

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 is non-diversified, which means that it may hold larger positions in a smaller number of issuers than a diversified fund. The Fund’s subadviser is Loomis, Sayles & Company, L.P. (Loomis Sayles).

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Initial Class shares returned -27.55%, outperforming the -29.14% 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, 2022, please see the Economic and Market Review, beginning on page 3.

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

For the one-year period ended December 31, 2022, stock selection in the communication services, health care, industrial, consumer staples, consumer discretionary, and financial sectors – as well as the Fund’s allocations to the health care, consumer discretionary, industrial, information technology, and financial sectors – contributed to relative returns. Stock selection in the information technology sector, as well as the Fund’s allocations to the communication services and consumer staples sectors, detracted from relative performance.

With respect to specific Fund holdings, Vertex Pharmaceuticals and Monster Beverage were the top contributors. As of the end of the fiscal period, Vertex Pharmaceuticals (“Vertex”) was a leader in creating therapies for patients suffering from cystic fibrosis (CF). Vertex reported financial results during the period that reflected the continued penetration of TRIKAFTA^®, its latest and most efficacious CF therapy. Fund management trimmed the Fund’s position in Vertex during the reporting period following the strong performance. As of the end of the fiscal period, Monster Beverage was a leading marketer and distributor of energy drinks in the U.S. and internationally. The company reported strong sales growth during the period, but faced pressure on profitability due to materials cost inflation, increased logistics costs, and can shortages. In the U.S., the company returned to share gains and market share leadership at fiscal year-end, despite increasing pricing by 6% in September 2022. Outside of the U.S., Monster continued to take market share and demonstrated impressive sales growth during the fiscal year. Fund management trimmed the Fund’s position in Monster Beverage during the reporting period following strong price performance.

Fund holdings that hampered performance the most during the reporting period were Meta Platforms and Nvidia. Meta Platforms operates online social networking platforms that allow people to connect, share, and interact with friends and communities. Over the past year, Meta faced headwinds arising from privacy restrictions imposed by Apple, the continued impact of macro weakness on advertising spending, and elevated investments, including a transition to a new product format – short-form video – where monetization was lower. Fund management took advantage of near-term market weakness to add to the Fund’s position in Meta on multiple occasions during the fiscal year. Nvidia is a world leader in graphic processing units (GPUs), which enable computers to produce and utilize highly realistic 3D graphic imagery. Nvidia shares were under pressure throughout 2022, given the weak market backdrop, despite reported financial results that were generally better than consensus expectations – and included multiple quarterly revenue records in the company’s gaming, data center, and professional visualization segments. However, for the last two quarters of 2022, the company experienced lower demand for its gaming cards, which reflected global demand for PCs returning to pre-pandemic levels after a period of excess, and the impact of macroeconomic weakness and COVID-19 restrictions on consumer spending in China. In late August, Nvidia also reported that the U.S. government restricted its ability to sell its leading AI chips to China over concerns that the technology could be leveraged by the Chinese military. The company moved quickly to redesign and ship its A800 chip, which provides Chinese companies with a viable alternative that does not violate U.S. government restrictions.

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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 communication services, health care, industrial, and financial sectors – and underweight in the information technology, consumer staples, and consumer discretionary sectors. The Fund did not have exposure to stocks in the energy, 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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55

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.

56

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, 2022?

The Fund’s Initial Class shares returned -12.05%, significantly outperforming the -18.11% 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 also outperformed the -13.01% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

Derivatives are securities that derive their value from the performance of one or more other investments and take the form of a contract between two or more parties. Derivatives can be used for hedging, speculation, or both.

The Fund began 2022 with full index put option coverage. As the equity market began its decline early in the year and implied volatility climbed, the Fund’s investment team began to identify opportunities to monetize higher volatility being priced into index put contracts, preserve index put gains in the event of a sudden and sharp market recovery, and to help position the Fund for attractive outcomes in a wider range of market scenarios. Fund management made these adjustments while keeping the Fund’s market exposure relatively consistent with its historical risk profile.

During the first quarter of 2022, the investment team reduced the Fund’s put coverage to an intra-quarter low range of 65% to 80% before incrementally adding index put options and restoring full put coverage by the quarter-end. During the second quarter, active adjustments were aimed at preserving index put gains in the event of a sudden and sharp market recovery, while maintaining the Fund’s typical risk profile. Put coverage reached an intra-quarter low range of 65% to 80%, a range that was maintained from mid-May through the end of the second quarter. In the third quarter, Fund management executed adjustments to put coverage in an effort to position the Fund for attractive outcomes in a wide range of market scenarios, while keeping the Fund’s market exposure relatively consistent. Put coverage reached an intra-quarter high range of 80% to 95% before adjustments in September brought coverage into a range of 65% to 80%, a level maintained through the end of the third quarter. During the final quarter of 2022, the investment team increased the Fund’s put coverage to a range of 80% to 95% on October 31 and restored full put coverage on November 8, which was maintained through December 31. Fund management executed the increases in put coverage in tandem with an adjustment to existing index put positions. These changes improved the loss mitigation potential of the index put portfolio, while lowering the overall potential annualized cost of puts. Index put option contracts were traded in advance of their expirations, while keeping weighted-average time to expiration relatively extended.

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The Fund maintained a portfolio of written index call options on the full value of its equity holdings over the course of the year, while making active adjustments to positions in response to deteriorating market conditions and opportunistically taking advantage of the higher implied volatility that was priced into longer-dated contracts to enhance cash flow potential. The term structure of volatility pricing was highly dynamic over the year and the investment team generally extended weighted-average time to expiration when term structure was steep and shortened when term structure was inverted or flat.

Subadviser outlook

Based on Gateway’s historic experience in the market, in Gateway’s view, the equity market has delivered well-above-average returns after drawdowns exceeding 20%. On the other hand, Gateway believes that investors who worry that stocks will have difficulty delivering enough near-term earnings growth to justify still-lofty valuations can justify their concerns in more ways than one. In particular, in Gateway’s view, as of the end of the fiscal period, supply chains and labor markets had yet to reach full repair and recent data as of the end of the fiscal period has shown that Americans were spending down their COVID savings. Consequently, Fund management believes that consumer balance sheets could deteriorate in short order, putting a damper on consumer demand and diminishing a key driver of economic growth.

Fund management notes that elevated equity market volatility and higher short-term interest rates increase index call option premiums like those written by the Fund. In Fund management’s view, higher index call option premiums could potentially improve the net cash flow generated by the Fund’s two-part option strategy. If current levels of volatility and interest rates persist, or move higher, Fund management believes that the Fund’s net cash flow may continue to be an attractive source of lower-risk participation in a potential equity market recovery, while possibly providing downside protection if there are additional losses between the end of the 2022 fiscal year and the ultimate recovery of the equity market.

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59

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.

60

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 78% of the Fund’s portfolio; and Wellington Management Company LLP (Wellington Management), which managed approximately 22% of the Fund’s portfolio, as of December 31, 2022. In addition, T. Rowe Price Investment Management serves as a sub-subadviser for the portion of the portfolio subadvised by T. Rowe Price.

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Initial Class shares returned -25.11%, outperforming the -26.72% 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 Initial Class shares -25.11% return significantly underperformed the -13.06% 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, 2022, 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, 2022, 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, information technology, health care, and communication services aided relative returns, while the energy and financial sectors detracted from the Fund’s relative performance. The information technology sector was a significant contributor to the Fund’s relative performance, due to stock selection and an underweight position, relative to the benchmark. Shares of Fund component holding KLA Corporation, a capital equipment company that provides control systems for the semiconductor industry, held up better than industry peers over the fiscal period. In health care, security selection had a positive impact on relative results, driven by Hologic, a medical technology company focused on women’s health that makes screening, detection, and treatment products. Communication services also aided the Fund’s relative returns, owing to an underweight allocation to the sector, coupled with favorable stock choices. In contrast, an underweight allocation to the energy sector detracted from the Fund’s relative performance. The financial sector also detracted, due to adverse security choices, although this was partially offset by an overweight allocation to the sector.

With respect to the Wellington Management Fund component, Fund component holdings that were top individual contributors to relative performance during the period included Gartner (information technology) and BWX Technologies (industrials). Gartner, an IT research and advisory services company, saw its share price increase after the company reported second-quarter 2022 earnings that beat expectations, driven by double-digit growth in contract value, revenue, and adjusted earnings-per-share. The share price of BWX Technologies – a nuclear components and fuel provider for the commercial nuclear power industry – rose over the fiscal period, as defense companies and weapon manufacturers benefited from increases in government defense budgets in the aftermath of Russia’s invasion of Ukraine. Fund component holdings that detracted most from relative returns during the reporting period included Omnicell (health care) and Align Technology (health care). The share price of Omnicell, a medication management software provider, fell sharply after the company released second-quarter results that missed expectations due to delivery delays. Align Technology is a leader in the clear and removable teeth aligner market with their Invisalign System. Their share price declined after management missed consensus estimates amid lower visibility.

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Subadviser outlook

Based on T. Rowe Price’s historic experience in the market, T. Rowe Price believes that prospects for U.S. equities will continue to be murky as we head into 2023, with the continued challenging economic backdrop. While Fund management notes that they are unsure if the market will fall to new lows in the upcoming fiscal year, they believe that much depends on the Federal Reserve (the “Fed”) and the world’s other major central banks as they continue efforts to bring inflation under control by hiking interest rates and draining liquidity from the markets. While T. Rowe Price, based on its historic experience in the market, has observed that Fed escalation cycles generally result in market underperformance, especially when inflation is running high, their view is that investors should not assume that a deep downturn is inevitable. Regardless of the environment, T. Rowe Price’s focus remains on owning quality companies with durable growth prospects and prudent balance sheets.

Wellington Management believes the volatile market environment has created more potential opportunities for active management to generate excess return. Near term, Fund management expects an increasingly challenging macroeconomic backdrop, given the Fed’s resolve to tame inflation at the cost of lower growth. However, the resilience of the labor market and early signs of supply chain bottlenecks easing give Wellington Management some confidence in the growth outlook beyond the immediate future. Fund management is increasingly focused on identifying higher-quality businesses that, in their opinion, could be more resilient during a down cycle, while having the potential to outperform as the environment stabilizes and turns more favorable.

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63

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.

64

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, 2022?

The Fund’s Initial Class shares returned -1.33%, significantly outperforming the -12.03% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, stock choices in the health care sector positively impacted the Fund’s performance, relative to the benchmark, particularly in the health care providers and services industry. Stock selection in the information technology sector, and within the IT services industry in particular, also benefited the Fund’s performance. In contrast, security selection in the energy sector detracted from the Fund’s relative results. A lack of exposure to Occidental Petroleum and other names from the oil, gas, and consumable fuels industry also hindered the Fund’s performance.

Fund holdings that were key contributors to performance during the reporting period included Reinsurance Group of America and Devon Energy. Global life and health reinsurance company Reinsurance Group of America reported better-than-expected quarterly earnings throughout the fiscal period, with strong core business performance. The company also reported better-than-expected COVID-19-related losses throughout the fiscal period. Shares of oil and gas exploration and production company Devon Energy outperformed, as commodity prices continued to rise amid a fundamentally tight market and geopolitical tensions. This boosted Devon’s free cash flow generation and helped the company make large dividend payments, buy back stock, and pay down debt.

Fund holdings that were key detractors included Advance Auto Parts and T. Rowe Price Group. Advance Auto Parts, an automotive replacement parts retailer, underperformed after announcing weaker-than-expected quarterly earnings and a reduced cash flow outlook for fiscal year 2023. These results were impacted by higher-than-expected inventory needs to serve its commercial automotive repair customers. Following outperformance in the third quarter of 2021, shares of asset management firm T. Rowe Price Group declined on lower equity markets. The company also reported continued outflows in assets under management in December.

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 reporting period, the Fund used currency forwards to hedge non-U.S. exposure. There was not a material impact on performance as a result of the Fund’s use of derivatives.

Subadviser outlook

The Fund seeks to invest in companies where Fund management believes the valuation does not reflect the quality and normal earnings power of the company. American Century’s process is generally based on individual security selection, but broad themes emerged during the reporting period. Their research led Fund management to several health care stocks that they believed to offer compelling risk/reward profiles. Due to Fund management’s belief in the potentially attractive valuations in consumer staples, as of fiscal year-end, the Fund held select companies in consumer staples that Fund management believes are trading at a discount to their intrinsic value. As of December 31, 2022, the Fund had an underweight allocation to consumer discretionary because of the difficulty of finding higher-quality companies with durable business models. The Fund also held an underweight allocation to information technology, largely due to valuations that Fund management viewed as stretched.

As we enter 2023, Fund management notes that we continue to face challenging macroeconomic and geopolitical conditions. In the event of a recession, Fund management believes that companies with low debt and steady revenues may be better positioned to grow and maintain their competitive edge, despite any economic headwinds.

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66

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.

67

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, 2022?

The Fund’s Initial Class shares returned -23.15%, outperforming the -26.36% 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 Initial Class shares -23.15% return underperformed the -20.44% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

Security selection was the primary driver of the Fund’s relative outperformance for the one-year period ended December 31, 2022. Selection was strongest within the health care, industrial, and information technology sectors – while weaker selection within communication services and utilities detracted from results. Sector allocation, a residual of the Fund’s bottom-up stock selection process, contributed to relative performance, led by the Fund’s underweight allocations, relative to the benchmark, to the health care, information technology, and consumer discretionary sectors. This was partially offset by underweight allocations to the energy and utilities sectors.

Fund holdings that were top relative contributors to the Fund’s performance during the period included First Solar (energy) and Viper Energy Partners (energy). First Solar, a manufacturer of solar panels, was both the top relative and absolute contributor to the Fund’s performance. Shares of the company climbed higher during the period after the company experienced strong tailwinds following the signing of the Inflation Reduction Act, which includes a significant investment in climate and energy policy. Fund management eliminated the position during the period. Shares of Viper Energy Partners – which owns, acquires, and exploits oil and natural gas properties – traded higher after the company reported earnings above expectations, driven by an increase in oil-equivalent production volumes and higher realizations of commodity prices.

Fund holdings that were among the top relative detractors for the period included Rapid7 (information technology) and Omnicell (health care). Rapid7 was both the top relative and absolute detractor. Rapid7 shares fell during the period after the cybersecurity solutions provider reported earnings results below expectations and sold off along with the software sector more broadly. Shares of Omnicell, a multinational health care technology company, fell during the period, as the company delivered disappointing third-quarter results and lowered its fiscal-year guidance. Demand for the company’s point-of-care products was delayed, impacted by labor challenges and deferred bookings.

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Subadviser outlook

Fund management notes that, in their view, 2022 was categorized by market volatility unlike anything experienced in the last several years, if not decades. A land-based war in Ukraine, aggressive Federal Reserve (the “Fed”) tightening, and an inflation report in excess of 9% are just a few examples of the conditions causing volatility. While, in Fund management’s view, investors seemed braced for a recession at fiscal year-end, Fund management believes that, as of the end of the fiscal year, the timing and magnitude of any recession are still unknown. In Fund management’s view, the large market swings experienced in 2022 are a result of market participants weighing the impacts of persistent inflation, recession, and the Fed’s reaction function. Given this uncertainty, at fiscal year-end, Fund management planned to remain disciplined within the Fund’s upside/downside valuation framework, balancing exposures to emerging and re-emerging growth companies. At the same time, they were positioning the Fund to be able to recover strongly when the market turns positive.

At the end of 2022, the Fund held its largest overweight allocations to the industrials and health care sectors and its greatest underweight allocations to the information technology, utilities, and materials sectors. As compared to 2021, Fund management believes that the most notable shifts in the Fund’s positioning included increasing the Fund’s allocations to health care and consumer staples and decreasing its exposure to information technology.

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70

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 Small Company Value Fund, and who is the Fund’s subadviser?

The Fund seeks long-term capital appreciation by investing primarily in equity securities 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 the 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 American Century Investment Management, Inc. (American Century).

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Class II shares returned -14.78%, underperforming the -14.48% return of the Russell 2000 Value Index (the “benchmark”), which measures the performance of the small-cap value segment of the U.S. equity universe. It includes those Russell 2000 Index companies with lower price-to-book ratios and lower forecasted growth values. The Fund outperformed the -20.44% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, the benchmark’s worst-performing sectors were communication services and health care. The Fund held underweight allocations to both sectors, relative to the benchmark, which added to the Fund’s relative returns. The best-performing sectors in the benchmark were the energy and utilities sectors. The Fund’s underweight positions in both sectors was detrimental to the Fund’s full-year results.

Hampering the Fund’s performance for the year were its allocations to, and selection decisions within, the energy sector. An overweight allocation to the information technology sector also detracted for the fiscal period, as did stock selections in the consumer staples sector. In the energy sector, the Fund’s large underweight allocation to the oil, gas, and consumable fuels industry was a leading source of underperformance for the fiscal period, but a lack of exposure to two strong-performing exploration and production companies, Antero Resources and Ovintiv, also detracted. In consumer staples, the Fund’s relatively large position in Spectrum Brands Holdings, which is not in the benchmark, was the main detractor for the fiscal period. This household goods company lagged during most of the period as general concern that the government would block the planned sale of its hardware and home improvement business weighed on the stock until late in the year.

On the positive side, the Fund primarily benefited from stock selection within, and its allocation to, the health care sector during the fiscal period. Fund holdings within, and its allocation to, the real estate sector also proved beneficial to the Fund’s returns for the fiscal period, while Fund holdings in the industrial and financial sectors also contributed. In health care, the Fund’s lack of exposure to the biotechnology industry was the primary driver of the contribution to the Fund’s performance, but in the health care providers and services industry, Fund holdings Patterson Cos. and Apria proved beneficial. In the real estate sector, an underweight to the equity real estate investment trust (REIT) industry was the primary driver of the contribution to the Fund’s performance, while a position in Getty Realty, a REIT that specializes in commercial real estate, also drove results. In the industrial sector, two Fund holdings in the building products industry, Cornerstone Building Brands and Colombian glassmaker Tecnoglass, which is not in the benchmark, were the main contributors to the Fund’s performance. In the financial sector, the decision to avoid exposure to the mortgage REITs industry was also advantageous.

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 2022, the Fund bought foreign exchange forward hedge contracts to offset the inherent currency risk of holding foreign securities. There was no material effect on performance from the use of these derivatives.

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Subadviser outlook

The Fund generally seeks to invest in companies where American Century believes the valuation does not reflect the quality and normal earnings power of the company. American Century’s process is based on individual security selection, but broad themes have emerged. As of December 31, 2022, the Fund’s largest overweight was in the information technology sector, driven by Fund management’s conviction in a number of unique and attractively valued opportunities. The Fund’s largest underweight was in the health care sector, on Fund management’s belief that valuations in the space were not presenting attractive risk/reward opportunities. A significant portion of the underweight in the health care sector was driven by the Fund’s lack of exposure to the biotechnology industry, which saw a material reweighting higher with the rebalancing of the benchmark at the end of the second quarter of 2022.

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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.

* 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 Small/Mid Cap Value Fund, and who is the Fund’s subadviser?

The Fund seeks long-term total return by investing primarily in securities 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 securities of small- and mid-cap companies. The Fund’s subadviser is AllianceBernstein L.P. (AllianceBernstein).

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Initial Class Shares returned -15.69%, underperforming the -13.08% return of the Russell 2500^TM Value Index (the “benchmark), which measures the performance of the small- to mid-cap value segment of the U.S. equity universe. It includes Russell 2500 Index companies with lower price-to-book and lower forecasted growth values.

For a discussion on the economic and market environment during the 12-month period ended December 31, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the one-year period ended December 31, 2022, both security and sector selection detracted from the Fund’s relative performance. Security selection within the consumer staples sector detracted from, whereas stock selection in the technology sector contributed to, the Fund’s performance. An underweight allocation, relative to the benchmark, to the energy sector hampered the Fund’s returns, while an underweight allocation to the real estate sector contributed.

With respect to specific Fund holdings, Hain Celestial (an American food company whose main focus is natural foods and botanically based personal care products) detracted from the Fund’s performance, after reporting disappointing fiscal third- and fourth-quarter results. In 2022, the company faced challenges as a result of cost inflation, supply-chain headwinds, and weakness in European consumer spending. Contract research organization Syneos Health also detracted from the Fund’s performance after reporting disappointing third-quarter 2022 results and lowering its estimates for 2023. The company’s forward guidance was predicated on weak bookings due to reduced spending by its large and mid-size pharmaceutical customers for contracted research services. Tire manufacturer Goodyear Tire & Rubber Company declined due to investor concerns about the company’s ability to raise prices to offset cost inflation, detracting from the Fund’s performance. The company beat estimates for the first two quarters of 2022, but missed third-quarter 2022 estimates and gave a disappointing fourth-quarter outlook.

Certain Fund holdings contributed to the Fund’s performance during the year. These included HF Sinclair, an oil refiner and manufacturer of lubricants, which benefited from a sharp increase in refining margins driven by turmoil in the energy markets after the Russian invasion of Ukraine. The company’s shares were additionally rewarded for the successful closing of the acquisition of The Sinclair Companies by HollyFrontier, a subsidiary of HF Sinclair. Acadia Healthcare, a behavioral health care provider, contributed to the Fund’s performance after reporting strong second-quarter 2022 earnings. Coterra Energy, a domestic energy exploration and production company, also helped to drive the Fund’s full-year results. The company benefited from the broad outperformance of the energy industry during the first half of 2022.

Subadviser outlook

Based on Fund management’s historic experience, Fund management believes that the past three years have been among the most volatile in recent memory. The market has grappled with shocks ranging from a global pandemic to the return of inflation. Certain of investors’ long-standing assumptions have come into question – with globalization seeming to reverse, energy and supply chain security driving company and countries’ spending, and a new era of structurally higher interest rates likely. While Fund management expects volatility to persist, they believe it could be reduced relative to the past few years. In their view, equity performance in the fourth quarter of 2022 seems to support this, as markets cheered improved inflationary data. While Fund management expects further shocks in 2023, their belief is that these market moves could suggest investors have begun to adjust to this new “normal.”

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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.

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 Sustainable Equity Fund, formerly known as 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 sustainable equity securities. Equity securities may include common stock, preferred stock, securities convertible into common or preferred stock, rights, and warrants. The Fund’s subadviser currently considers sustainable securities to be those to which the subadviser’s proprietary model assigns an ESG score that is in the top three quartiles of the environmental, social, and governance (“ESG”) scores the model assigns to all of the securities in the Fund’s benchmark, the S&P 500^® Index. The Fund’s subadviser is American Century Investment Management, Inc. (American Century). Effective April 29, 2022, American Century replaced Massachusetts Financial Services Company (MFS) as subadviser of the Fund.

How did the Fund perform during the 12 months ended December 31, 2022?

The Fund’s Initial Class shares returned -17.01%, outperforming the -18.11% 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, 2022, please see the Economic and Market Overview, beginning on page 3.

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

For the period of the fiscal year during which MFS served as subadviser of the Fund (January 1, 2022 - April 28, 2022), security selection in both the information technology and communication services sectors contributed to the Fund’s relative performance. Within information technology, not owning shares of both computer graphics processor maker NVIDIA and digital payment technology developer PayPal proved positive for the Fund. In addition, Fund holding Amdocs (a billing software company), which is not a benchmark constituent, supported the Fund’s relative results. Within the communication services sector, not owning shares of social networking service provider Meta Platforms also aided the Fund’s relative returns. Fund holdings in other sectors that bolstered relative performance included oil and gas company ConocoPhillips, biotechnology company Vertex Pharmaceuticals, engineered solutions provider for the aerospace and transportation industries Howmet Aerospace, pharmaceutical company Merck, and retailer Target. Additionally, not owning streaming services provider Netflix further helped relative returns. Detracting from the Fund’s performance relative to the benchmark was security selection in the financial sector. There, not owning shares of insurance and investment firm Berkshire Hathaway – as well as overweight positions in securities exchange services provider NASDAQ and global financial services firm JPMorgan Chase – held back relative returns. The Fund’s underweight position in the strong-performing energy sector also hindered the Fund’s relative results, as did not owning shares of integrated energy companies ExxonMobil and Chevron. Fund holdings in other sectors that hampered relative performance included Irish clinical research provider ICON (not a benchmark constituent) and overweight positions in technology company Alphabet, building controls and systems supplier Johnson Controls International, and software company Adobe Systems. Additionally, not owning shares of health insurance and Medicare/Medicaid provider UnitedHealth Group further hurt the Fund’s relative returns.

For the period of the fiscal year during which American Century served as subadviser of the Fund (April 29, 2022 - December 31, 2022), the Fund’s largest overweight sectors relative to the benchmark were information technology, industrial, and health care. Fund holdings in the energy sector led the Fund’s outperformance of the benchmark. Oil field services company Schlumberger reported strong results across all divisions and geographies during the fiscal period, with higher revenues, earnings, and stronger margins than expected. ConocoPhillips reported solid earnings and increased its 2022 capital return guidance during the fiscal period. The Fund’s lack of exposure to Meta Platforms benefited results, as Facebook’s parent company was hurt more by both Apple iOS platform changes and TikTok competition than other digital advertising platforms over the course of the fiscal period. Managed care companies, including Cigna, benefited from what, in Fund management’s view, many investors perceived to be their defensive profile, meaning the company is believed to be relatively insulated from both rising prices and recession risk. Utility company NextEra Energy outperformed during the fiscal period, given a favorable outlook for its renewable energy development business, further strengthened by the passage of the Inflation Reduction Act of 2022.

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Fund holdings in the real estate sector detracted during the reporting period, led by warehouse real estate investment trust Prologis, which suffered on announcements from Amazon and FedEx that they were reducing excess capacity (which hampered the industry overall). Rising interest rates and a strong dollar also weighed on sector performance during the fiscal period. Other significant detractors included not owning oil giant ExxonMobil, which outperformed during the fiscal period due to rising oil prices. Packaging company Ball lagged after reporting disappointing revenue and earnings during the fiscal period, with slowing customer demand leading to weaker volume growth expectations and a decision to reduce production capacity. Medical device maker Edwards Lifesciences underperformed during the fiscal period, as the recovery in transcatheter aortic valve replacement (TAVR) procedures was slower than expected. 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 derivatives had no material impact on performance during the reporting period.

Subadviser outlook