Summary Prospectus by Investment Company - Form 497K

INVESTMENT OBJECTIVE

The Fund seeks long-term capital growth.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund. The expenses in the table do not reflect deductions at the separate account level or contract level for any charges that may be incurred under a variable life insurance or variable annuity contract. If these charges were reflected, the fees and expenses in the table would be higher.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

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(1)

The expenses in the above table reflect a written agreement by MML Advisers to cap the fees and expenses of the Fund (other than extraordinary legal and other expenses, Acquired Fund Fees and Expenses, interest expense, expenses related to borrowings, securities lending, leverage, taxes, and brokerage, short sale dividend and loan expense, or other non-recurring or unusual expenses such as organizational expenses and shareholder meeting expenses, as applicable) through April 30, 2025, to the extent that Total Annual Fund Operating Expenses after Expense Reimbursement would otherwise exceed 1.25% and 1.50% for Class II and Service Class I shares, respectively. The Total Annual Fund Operating Expenses after Expense Reimbursement shown in the above table may exceed these amounts, because, as noted in the previous sentence certain fees and expenses are excluded from the cap. The agreement can only be terminated by mutual consent of the Board of Trustees on behalf of the Fund and MML Advisers.

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Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It assumes that you invest $10,000 in each share class of the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment earns a 5% return each year and that the Fund's operating expenses are exactly as described in the preceding table. If separate account or variable life insurance or variable annuity contract expenses were included, overall expenses would be higher. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 35% of the average value of its portfolio.

INVESTMENTS, RISKS, AND PERFORMANCE​

Principal Investment Strategies

The Fund mainly invests in common stocks of issuers in developing and emerging markets throughout the world and at times it may invest up to 100% of its total assets in foreign securities. Under normal market conditions, the Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in

equity securities of issuers whose principal activities are in a developing (or emerging) market, i.e. are in a developing market or are economically tied to a developing market country. The Fund will invest in at least three developing markets. The Fund focuses on companies that the Fund's subadviser, Invesco Advisers, Inc. ("Invesco Advisers"), believes have above-average earnings growth. The Fund may at times have significant exposure to one or more industries or sectors. The Fund may hold a portion of its assets in cash or cash equivalents.

In general, countries may be considered developing or emerging markets if they are included in any one of the MSCI emerging markets indexes or excluded from an index that captures representation across developed market countries, classified as a developing or emerging market, or classified under a similar or corresponding classification, by organizations such as the World Bank and the International Monetary Fund, or have economies, industries, and stock markets with similar characteristics as such countries. For purposes of the Fund's investments, a determination that an issuer is economically tied to a developing market country is based on factors including, but not limited to, geographic location of its primary trading markets, location of its assets, its domicile or its principal offices, or whether it receives revenues from a developing market. Such a determination can also be based, in whole or in part, on inclusion of an issuer or its securities in an index representative of developing or emerging markets, or on its "country of risk" being a developing market country as determined by a third-party service provider.

The Fund can invest in common and preferred stocks and debt securities of U.S. companies. It can also hold U.S. corporate and government debt securities for defensive and liquidity purposes. In addition to common and preferred stocks, the Fund can invest in other equity or "equity equivalents" securities such as convertible securities, rights, or warrants. The Fund may purchase American Depositary Shares ("ADS") as part of American Depositary Receipt ("ADR") issuances. Under normal market conditions, the Fund currently does not expect to invest a significant amount of its assets in securities of U.S. issuers or debt of any issuer. The Fund may use derivatives, including futures contracts, forward contracts, and options, to seek to enhance the Fund's investment return or for hedging purposes. The Fund is not required to use derivatives in seeking its investment

objective or for hedging and might not do so. Use of derivatives by the Fund may create investment leverage.

The Fund may invest in illiquid or thinly traded securities. The Fund may also invest in securities that are subject to resale restrictions such as those contained in Rule 144A promulgated under the Securities Act of 1933, as amended.

The Fund may invest directly in certain eligible China A Shares through Stock Connect (a securities trading and clearing program designed to achieve mutual stock market access between the People's Republic of China ("PRC") and Hong Kong).

In selecting investments for the Fund, Invesco Advisers evaluates investment opportunities on a company-by-company basis. This approach includes fundamental analysis of a company's financial statements, management record, capital structure, operations, product development, and competitive position in its industry. Invesco Advisers also looks for newer or established businesses that it believes are entering into a growth cycle, have the potential for accelerating earnings growth or cash flow, and possess reasonable valuations. Invesco Advisers considers the effect of worldwide trends on the growth of particular business sectors and looks for companies that may benefit from those trends and seeks a diverse mix of industries and countries to help reduce the risks of foreign investing, such as currency fluctuations and stock market volatility. Invesco Advisers may invest in growth companies of different capitalization ranges in any developing market country. Invesco Advisers monitors individual issuers for changes in the factors above, which may trigger a decision to sell a security.

Principal Risks

The following are the Principal Risks of the Fund. The value of your investment in the Fund could go down as well as up. You can lose money by investing in the Fund. Certain risks relating to instruments and strategies used in the management of the Fund are placed first. The significance of any specific risk to an investment in the Fund will vary over time, depending on the composition of the Fund's portfolio, market conditions, and other factors. You should read all of the risk information presented below carefully, because any one or more of these risks may result in losses to the Fund.

Equity Securities Risk Although stocks may have the potential to outperform other asset classes

over the long term, their prices tend to fluctuate more dramatically over the shorter term. These movements may result from factors affecting individual companies, or from broader influences like changes in interest rates, market conditions, or investor confidence, or announcements of economic, political, or financial information.

Foreign Investment Risk; Emerging Markets Risk; Currency Risk Investments in securities of foreign issuers, securities of companies with significant foreign exposure, and foreign currencies can involve additional risks relating to market, industry, political, regulatory, public health, and other conditions. Political, social, diplomatic, and economic developments, U.S. and foreign government action, or threat thereof, such as the imposition of currency or capital blockages, controls, or tariffs, economic and trade sanctions or embargoes, security trading suspensions, entering or exiting trade or other intergovernmental agreements, or the expropriation or nationalization of assets in a particular country, can cause dramatic declines in certain or all securities with exposure to that country and other countries. Sanctions, or the threat of sanctions, may cause volatility in regional and global markets and may negatively impact the performance of various sectors and industries, as well as companies in other countries, which could have a negative effect on the performance of the Fund. In the event of nationalization, expropriation, confiscation, or other government action, intervention, or restriction, the Fund could lose its entire investment in a particular foreign issuer or country. There may be quotas or other limits on the ability of the Fund (or clients of the Fund's investment adviser or subadviser) to invest or maintain investments in securities of issuers in certain countries. Enforcing legal rights can be more difficult, costly, and limited in certain foreign countries and with respect to certain types of investments, and can be particularly difficult against foreign governments. Because non-U.S. securities are normally denominated and traded in currencies other than the U.S. dollar, the value of the Fund's assets may be affected favorably or unfavorably by changes in currency exchange rates, exchange control regulations, and restrictions or prohibitions on the repatriation of non-U.S. currencies. Income and gains with respect to investments in certain countries may be subject to withholding and other taxes. There may be less information publicly available about a non-U.S. company than about a U.S. company, and many non-U.S. companies are not subject to accounting,

auditing, and financial reporting standards, regulatory framework and practices comparable to those in the U.S. The securities of some non-U.S. companies, especially those in emerging markets, are less liquid and at times more volatile than securities of comparable U.S. companies. Emerging markets securities are subject to greater risks than securities issued in developed foreign markets, including less liquidity, less stringent investor protection and disclosure standards, less reliable settlement practices, greater price volatility, higher relative rates of inflation, greater political, economic, and social instability, greater custody and operational risks, greater risk of new or inconsistent government treatment of or restrictions on issuers and instruments, and greater volatility in currency exchange rates, and are more susceptible to environmental problems. Many emerging market countries are highly reliant on international trade and exports, including the export of commodities. Their economies may be significantly impacted by fluctuations in commodity prices and the global demand for certain commodities. In addition, pandemics and outbreaks of contagious diseases may exacerbate pre-existing problems in emerging market countries with less established health care systems. Frontier markets, a subset of emerging markets, generally have smaller economies and less mature capital markets than emerging markets. As a result, the risks of investing in emerging market countries are magnified in frontier market countries. Frontier markets are more susceptible to having abrupt changes in currency values, less mature markets and settlement practices, and lower trading volumes that could lead to greater price volatility and illiquidity. Non-U.S. transaction costs, such as brokerage commissions and custody costs, may be higher than in the United States. In addition, foreign markets can react differently to market, economic, industry, political, regulatory, geopolitical, public health, and other conditions than the U.S. market.

China Investment Risk Investments in China (including Chinese companies listed on U.S. and Hong Kong exchanges), Hong Kong, and Taiwan, involve certain risks and considerations not typically associated with investments in U.S. companies, such as greater government control over the economy, political and legal uncertainty, currency fluctuations or blockages, the risk that the Chinese government may decide not to continue to support economic reform programs, and the risk of nationalization or expropriation of assets. Additionally, the securities markets of China,

Hong Kong, and Taiwan are emerging markets subject to the special risks applicable to emerging market countries.

Derivatives Risk Derivatives can be highly volatile and involve risks different from, and potentially greater than, direct investments, including risks of imperfect correlation between the value of derivatives and underlying assets, counterparty default, potential losses that partially or completely offset gains, and illiquidity. Derivatives can create investment leverage. Losses from derivatives can be substantially greater than the derivatives' original cost and can sometimes be unlimited. If the value of a derivative does not correlate well with the particular market or asset class the derivative is designed to provide exposure to, the derivative may not have the effect or benefit anticipated. Derivatives can also reduce the opportunity for gains or result in losses by offsetting positive returns in other investments. Many derivatives are traded in the over-the-counter market and not on exchanges.

Growth Company Risk The prices of growth securities are often highly sensitive to market fluctuations because of their heavy dependence on future earnings or cash flow expectations, and can be more volatile than the market in general.

Large Company Risk Large-capitalization stocks as a group could fall out of favor with the market, causing the Fund's investments in large-capitalization stocks to underperform investments that focus on small- or medium-capitalization stocks. Larger, more established companies may be slow to respond to challenges and may grow more slowly than smaller companies.

Small and Mid-Cap Company Risk Market risk and liquidity risk are particularly pronounced for securities of small and medium-sized companies, which may trade less frequently and in smaller volumes than more widely-held securities, and may fluctuate in price more than other securities. Their shares can be less liquid than those of larger companies, especially during market declines. Small and medium-sized companies may have limited product lines, markets, or financial resources and may be dependent on a limited management group; they may have been recently organized and have little or no track record of success.

Stock Connect Risk The Fund may invest in China A Shares through Stock Connect, which is subject to sudden changes in quota limitations, application

of trading suspensions, price fluctuations during times when Stock Connect is not trading, operational risk, clearing and settlement risk, and regulatory and taxation risk.

Cash Position Risk If the Fund holds a significant portion of its assets in cash or cash equivalents, its investment returns may be adversely affected and the Fund may not achieve its investment objective.

Convertible Securities Risk Convertible securities are subject to the risks of both debt instruments and equity securities. The price of a convertible security may change in response to changes in price of the underlying equity security, the credit quality of the issuer, and interest rates. In general, the values of convertible securities tend to decline as interest rates rise and to rise when interest rates fall. A convertible security generally has less potential for gain or loss than the underlying equity security.

Credit Risk Credit risk is the risk that an issuer, guarantor, or liquidity provider of a fixed income security held by the Fund may be unable or unwilling, or may be perceived (whether by market participants, ratings agencies, pricing services or otherwise) as unable or unwilling, to make timely principal and/or interest payments, or to otherwise honor its obligations. The Fund may also be exposed to the credit risk of its counterparty to repurchase agreements, reverse repurchase agreements, swap transactions, and other derivatives transactions, and to the counterparty's ability or willingness to perform in accordance with the terms of the transaction. The value of such transactions to the Fund will depend on the willingness and ability of the counterparty to perform its obligations, including among other things the obligation to return collateral or margin to the Fund. If a counterparty becomes bankrupt or otherwise fails to perform its obligations under a derivative contract due to financial difficulties, the Fund may experience significant delays in obtaining any recovery under the derivative contract in a bankruptcy or other reorganization proceeding. The Fund may obtain only a limited recovery or may obtain no recovery in such circumstances.

Fixed Income Securities Risk The values of fixed income securities typically will decline during periods of rising interest rates, and can also decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral assets, or changes in market, economic, industry, political, regulatory, public health, and

other conditions affecting a particular type of security or issuer or fixed income securities generally. Certain events, such as market or economic developments, regulatory or government actions, natural disasters, pandemics, terrorist attacks, war, and other geopolitical events can have a dramatic adverse effect on the debt market and the overall liquidity of the market for fixed income securities. During those periods, the Fund may experience high levels of shareholder redemptions, and may have to sell securities at times when the Fund would otherwise not do so, and potentially at unfavorable prices. Certain securities may be difficult to value during such periods. Fixed income securities are subject to interest rate risk (the risk that the value of a fixed income security will fall when interest rates rise), extension risk (the risk that the average life of a security will be extended through a slowing of principal payments), prepayment risk (the risk that a security will be prepaid and the Fund will be required to reinvest at a less favorable rate), duration risk (the risk that longer-term securities may be more sensitive to interest rate changes), inflation risk (the risk that as inflation increases, the present value of the Fund's fixed income investment typically will decline), and credit risk.

Geographic Focus Risk When the Fund focuses investments on a particular country, group of countries, or geographic region, its performance will be closely tied to the market, currency, economic, political, or regulatory conditions and developments in those countries or that region, and could be more volatile than the performance of more geographically diversified funds.

Hedging Risk The Fund's attempts at hedging and taking long and short positions in currencies may not be successful and could cause the Fund to lose money or fail to get the benefit of a gain on a hedged position. If expected changes to securities prices, interest rates, currency values, and exchange rates, or the creditworthiness of an issuer are not accurately predicted, the Fund could be in a worse position than if it had not entered into such transactions.

Liquidity Risk Certain securities may be difficult (or impossible) to sell or certain positions may be difficult to close out at a desirable time and price, and the Fund may be required to hold an illiquid investment that is declining in value, or it may be required to sell certain illiquid investments at a price or time that is not advantageous in order to meet redemptions or other cash needs. Some

securities may be subject to restrictions on resale. There can be no assurance that there will be a liquid market for instruments held by the Fund at any time. The Fund may not receive the proceeds from the sale of certain investments for an extended period.

Management and Operational Risk The Fund relies on the manager's investment analysis and its selection of investments to achieve its investment objective, and the Fund is subject to the risk that the manager's assessment of an investment is wrong. There can be no assurance that the Fund will achieve the intended results and the Fund may incur significant losses. The Fund also runs the risk that deficiencies in the investment adviser's, subadviser's, or another service provider's internal systems or controls will cause losses for the Fund or impair Fund operations.

Market Risk The value of the Fund's portfolio securities may decline, at times sharply and unpredictably, as a result of unfavorable market-induced changes affecting particular industries, sectors, or issuers. Stock and bond markets can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, public health, and other conditions, as well as investor perceptions of these conditions. The Fund is subject to risks affecting issuers, such as management performance, financial leverage, industry problems, and reduced demand for goods or services.

Preferred Stock Risk Like other equity securities, preferred stock is subject to the risk that its value may decrease based on actual or perceived changes in the business or financial condition of the issuer. In addition, changes in interest rates may adversely affect the value of a preferred stock that pays a fixed dividend. Preferred stocks are also subject to additional risks, such as potentially greater volatility and risks related to deferral, non-cumulative dividends, subordination, liquidity, limited voting rights, and special redemption rights.

Restricted Securities Risk The Fund may hold securities that are restricted as to resale under the U.S. federal securities laws, such as securities in certain privately held companies. Such securities may be highly illiquid and their values may experience significant volatility. Restricted securities may be difficult to value.

Sector Risk The Fund may allocate more of its assets to particular industries or to particular

economic, market, or industry sectors than to others. This could increase the volatility of the Fund's portfolio, and the Fund's performance may be more susceptible to developments affecting issuers in those industries or sectors than if the Fund invested more broadly.

U.S. Government Securities Risk Obligations of certain U.S. Government agencies and instrumentalities are not backed by the full faith and credit of the U.S. Government, and there can be no assurance that the U.S. Government would provide financial support to such agencies and instrumentalities.

Valuation Risk The Fund is subject to the risk of mispricing or improper valuation of its investments, in particular to the extent that its securities are fair valued.

Performance Information

The following bar chart and table provide some indication of the risks of investing in the Fund. The bar chart shows changes in the Fund's performance from year to year for Service Class I shares. The table shows how the Fund's average annual returns for 1, 5, and 10 years compare with those of a broad measure of market performance. Performance shown does not reflect the fees and expenses deducted under the variable life insurance or variable annuity contract through which you invest in the Fund. If these amounts were reflected, returns would be less than those shown. Past performance is not necessarily an indication of how the Fund will perform in the future.

Annual Performance

Service Class I Shares

Average Annual Total Returns

(for the periods ended December 31, 2023)

MANAGEMENT

Investment Adviser: MML Investment Advisers, LLC ("MML Advisers")

Subadviser(s): Invesco Advisers, Inc. ("Invesco Advisers")

Portfolio Manager(s):

Justin Leverenz, CFA is a Portfolio Manager at Invesco Advisers. He has managed the Fund since October 2013.

PURCHASE AND SALE OF FUND SHARES

Shares of the Fund are generally available to separate investment accounts of variable life insurance and variable annuity contracts offered by companies such as MassMutual. An investor should consult the company issuing the investor's variable life insurance or variable annuity contract to determine how to make redemptions.

TAX INFORMATION

Dividends and capital gain distributions are paid to the insurance company separate accounts. Variable life insurance and variable annuity contract owners should refer to the variable life insurance or variable annuity product prospectus or consult with their own tax adviser for information regarding the tax consequences of their investment.

PAYMENTS TO INSURANCE COMPANIES AND THEIR AFFILIATES

The Fund is not sold directly to the general public but instead is offered as an underlying investment option for variable insurance contracts. The Fund and its related companies may make payments to the sponsoring insurance company (or its affiliates) or other intermediary for distribution and/or other services. These payments may be a factor that the insurance company considers in including the Fund as an underlying investment option in the variable insurance contract or may create a conflict of interest by influencing the insurance company or other intermediary to recommend the variable insurance contract over another investment. The prospectus (or other offering document) for your variable insurance contract may contain additional information about these payments.