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Summary Prospectus May 1, 2024

MML Series Investment Fund

MML Small Cap Growth Equity Fund

Initial Class, Service Class

Before you invest, you may want to review the Fund’s prospectus, which contains more information about the Fund and its risks. You can find the Fund’s prospectus and other information about the Fund online at https://www.massmutual.com/funds. You can also get this information at no cost by calling 1-888-309-3539 or by sending an email request to fundinfo@massmutual.com.

INVESTMENT OBJECTIVE

This Fund seeks long-term capital appreciation.

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)

	Initial Class	Service Class
Management Fees	1.04%	1.04%
Distribution and Service (Rule 12b-1) Fees	None	0.25%
Other Expenses	0.07%	0.07%
Total Annual Fund Operating Expenses	1.11%	1.36%
Fee Waiver	(0.03%)	(0.03%)
Total Annual Fund Operating Expenses after Fee Waiver(1)	1.08%	1.33%

(1)

The expenses in the above table reflect a written agreement by MML Advisers to waive 0.03% of its management fees through April 30, 2025. The agreement can only be terminated by mutual consent of the Board of Trustees on behalf of the Fund and MML Advisers.

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:

	1 Year			3 Years			5 Years			10 Years
Initial Class		$	110		$	350		$	609		$	1,349
Service Class		$	135		$	428		$	742		$	1,632

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 39% of the average value of its portfolio.

INVESTMENTS, RISKS, AND PERFORMANCE

Principal Investment Strategies

The Fund invests 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 (as of February 29, 2024, between $22.04 million and $48.43 billion). Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stock, rights, and warrants. While most assets typically will be invested in common stocks

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of U.S. companies, the Fund also may invest up to 20% of its total assets in foreign securities, including emerging market securities. 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.

The Fund is managed by Wellington Management Company LLP (“Wellington Management”). Wellington Management employs a growth-based investment approach and may perform a number of analyses in considering whether to buy or sell a security for the Fund. Wellington Management uses a combination of fundamental and quantitative analyses to identify small-cap companies that it believes are experiencing or will experience rapid earnings or revenue growth. Wellington Management may consider selling a security for the Fund if, for example, in its judgment, target prices are reached, future upside potential is limited, company fundamentals are no longer attractive, superior purchase candidates are identified, or market capitalization ceilings are exceeded.

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.

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.

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,

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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.

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.

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.

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

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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.

Quantitative Models Risk The portfolio managers use quantitative models as part of the idea generation process. Quantitative models are based upon many factors that measure individual securities relative to each other. Such models may not produce the intended results and can be adversely affected by errors or imperfections in the factors or the data on which measurements are based, changing sources of market return or market risk, human error, or any technical issues with the design, construction, implementation, or maintenance of the models.

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.

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 Initial Class 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 and an additional index that provides a comparison for the Fund’s returns without regard to investment style (Russell 2000 Index). 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

Initial Class Shares

Highest Quarter:

4Q ’20,

32.36%

Lowest Quarter:

1Q ’20,

-28.67%

Average Annual Total Returns

(for the periods ended December 31, 2023)

		One Year			Five Years			Ten Years
Initial Class	MML Small Cap Growth Equity Fund		16.84	%		11.91	%		8.80	%
Service Class	MML Small Cap Growth Equity Fund		16.55	%		11.63	%		8.53	%
Russell 2000 Growth Index (reflects no deduction for fees, expenses, or taxes)			18.66	%		9.22	%		7.16	%
Russell 2000 Index (reflects no deduction for fees, expenses, or taxes)			16.93	%		9.97	%		7.16	%

MANAGEMENT

Investment Adviser: MML Investment Advisers, LLC (“MML Advisers”)

Subadviser(s): Wellington Management Company LLP (“Wellington Management”)

Portfolio Manager(s):

Daniel J. Fitzpatrick, CFA is a Senior Managing Director and Equity Portfolio Manager at Wellington Management. He has managed the Fund since November 2001.

Ranjit Ramachandran, CFA is a Managing Director and Equity Portfolio Manager at Wellington Management. He has managed the Fund since February 2022.

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.

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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.

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