Summary Prospectus by Investment Company (Form 497K)

MML Series Investment Fund

MML VIP BlackRock^®Equity Index Fund
(formerly known as MML Equity Index Fund)

Class I, Class II, Class III, Service Class I

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/product-performance/variable-insurance-funds. You can also get this information at no cost by calling 1-888-309-3539 or by sending an email request to [email protected].

INVESTMENT OBJECTIVE

The Fund seeks to provide investment results that correspond to the total return performance of publicly traded common stocks in the aggregate as represented by the S&P 500^® Index*.

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)

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 2% of the average value of its portfolio.

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INVESTMENTS, RISKS, AND PERFORMANCE

Principal Investment Strategies

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 S&P 500 Index (the "Index"). The Fund invests in the equity securities of companies included in the Index in weightings that approximate the relative composition of the securities contained in the Index, and in S&P 500 Index futures contracts. The Index is a widely recognized, unmanaged index representative of common stocks of larger capitalized U.S. companies. As of February 28, 2026, the market capitalization range of companies included in the Index was $5.01 billion to $4.31 trillion. If the securities represented in the Index were to become concentrated in any particular industry, the Fund's investments would likewise be concentrated in securities of issuers in that industry; the Index is not currently concentrated in any single industry.

The Fund is passively managed, which means it tries to replicate the investment composition and performance of the Index by using computer programs and statistical procedures. The Fund's  subadviser, BlackRock Investment Management, LLC ("BlackRock"), will buy and sell securities in response to changes in the Index. The Fund may use Index futures contracts, a type of derivative, to gain exposure to the Index in lieu of investing in cash, or to reduce its exposure to the Index while it sells the securities in its portfolio. Use of Index futures contracts by the Fund may create investment leverage. Because the Fund, unlike the Index, is subject to fees and transaction expenses, the Fund's returns are likely to be less than those of the Index. BlackRock expects that, under normal circumstances, the annual performance of the Fund, before fees and expenses, will track the performance of the Index within a 0.95 correlation coefficient.

The Fund intends to be diversified in approximately the same proportion as the Index is diversified. The Fund may become "non-diversified," as defined in the Investment Company Act of 1940, as amended (the "1940 Act"), solely as a result of a change in relative market capitalization or index weighting of one or more constituents of the Index. In these circumstances, the Fund may hold larger positions in a smaller number of issuers than a diversified fund. Shareholder approval will not be sought if the Fund becomes "non-diversified" due solely to a change in the relative market capitalization or index weighting of one or more constituents of the Index.

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.

Indexing Risk The Fund's performance may not track the performance of the index due to a number of factors, including fees and expenses of the Fund, the Fund's cash positions, and differences between securities held by the Fund and the securities comprising the index which may result from legal restrictions, costs, or liquidity constraints, especially during times when a sampling methodology is used.

Industry Concentration Risk The Fund may concentrate its assets in a particular industry or group of industries. This could increase the volatility of the Fund's portfolio, and the Fund's performance may be more susceptible to developments affecting issuers in that industry or group of industries than if the Fund invested more broadly.

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.

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.

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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.

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.

Non-Diversification Risk In seeking to track the Index, the Fund may become non-diversified solely as a result of a change in relative market capitalization or index weighting of one or more constituents of the Index. In such circumstances, because the Fund may invest a larger percentage of its assets in a single issuer or in a smaller number of issuers as compared to a diversified fund, the Fund's performance could be closely tied to the value of one issuer or a small number of issuers and could be more volatile than the performance of a diversified fund.

Passive Management Risk With an indexing strategy, there is no attempt to seek returns in excess of a benchmark index, to use defensive strategies, or to reduce the effects of any long-term poor investment performance. Therefore, the Fund would not necessarily buy or sell a security unless that security is added to, or removed from, the index, even if that security generally is underperforming.

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 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

Class I Shares

Average Annual Total Returns
(for the periods ended December 31, 2025)

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MANAGEMENT

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

Subadviser(s): BlackRock Investment Management, LLC ("BlackRock")

Portfolio Manager(s):

Jennifer Hsui, CFA is a Managing Director at BlackRock. She has managed the Fund since April 2025.

Peter Sietsema, CFA is a Managing Director at BlackRock. He has managed the Fund since May 2025.

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.

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