Summary Prospectus    February 1, 2024
as revised on February 12, 2024

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 Class R5 shares 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

INVESTMENTS, RISKS, AND PERFORMANCE​

Principal Investment Strategies

The Fund normally invests at least 99.5% of its total assets in cash, U.S. Government securities, and/or repurchase agreements fully collateralized by cash or U.S. Government securities.

In managing the Fund, the Fund’s subadviser, Barings LLC (“Barings”), intends to comply with Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”), which sets forth the requirements for money market funds regarding credit quality, diversification, liquidity, and maturity. The Fund seeks to maintain, but does not guarantee, a stable $1.00 share price.

Under normal circumstances, the Fund invests at least 80% of its net assets in U.S. Government securities and repurchase agreements that are fully collateralized by U.S. Government securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury.

Principal Risks

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor is not required to reimburse the Fund for losses, and you should not expect that the sponsor will provide financial support to the Fund at any time, including during periods of market stress.

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.

Money Market Instruments Risk The value of a money market instrument 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.

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.

Repurchase Agreement Risk  These transactions must be fully collateralized, but involve credit risk to a Fund if the other party should default on its obligation and the Fund is delayed or prevented from recovering the collateral.

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.

Inflation Risk The value of assets or income from the Fund’s investments will be less in the future as inflation decreases the value of money. As inflation increases, the value of the Fund’s assets

can decline as can the value of the Fund’s distributions. Inflation rates may change frequently and drastically as a result of various factors, including unexpected shifts in the domestic or global economy (or expectations that such policies will change), and the Fund’s investments may not keep pace with inflation, which may result in losses to the Fund’s investors.

LIBOR Transition and Other Reference Benchmarks Risk The London Interbank Offered Rate (“LIBOR”) was the offered rate for short-term Eurodollar deposits between major international banks. The terms of investments, financings, or other transactions (including certain derivatives transactions) to which the Fund may be a party have historically been tied to LIBOR. In connection with the global transition away from LIBOR led by regulators and market participants, LIBOR was last published on a representative basis at the end of June 2023. Alternative reference rates to LIBOR have been established in most major currencies and the transition to new reference rates continues. Markets in these new rates are developing, but questions around liquidity and how to appropriately mitigate any economic value transfer as a result of the transition remain a concern. The transition away from LIBOR and the use of replacement rates may adversely affect transactions that used LIBOR as a reference rate, financial institutions, funds, and other market participants that engaged in such transactions, and the financial markets generally. The impact of the transition away from LIBOR on the Fund or the financial instruments in which the Fund invests cannot yet be fully determined. In addition, interest rates or other types of rates and indexes which are classed as “benchmarks” have been the subject of ongoing national and international regulatory reform, including under the European Union regulation on indexes used as benchmarks in financial instruments and financial contracts (known as the “Benchmarks Regulation”). The Benchmarks Regulation has been enacted into United Kingdom law by virtue of the European Union (Withdrawal) Act 2018 (as amended), subject to amendments made by the Benchmarks (Amendment and Transitional Provision) (EU Exit) Regulations 2019 (SI 2019/657) and other statutory instruments. Following the implementation of these reforms, the manner of administration of benchmarks has changed and may further change in the future, with the result that relevant benchmarks may perform differently than in the past, the use of benchmarks that are not compliant with the new standards set by certain

supervised entities may be restricted, and certain benchmarks may be eliminated entirely. Additionally, there could be other consequences which cannot be predicted.

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.

Prepayment Risk Prepayment risk is the risk that principal of a debt obligation will be repaid at a faster rate than anticipated. In such a case, a Fund may lose the benefit of a favorable interest rate for the remainder of the term of the security in question, and may only be able to reinvest the amount of the prepayment at a less favorable rate.

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 R5 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. The Fund’s name, investment objective, and investment strategy changed on May 1, 2016 when the Fund changed from a money market fund to a government money market fund. Performance results shown were achieved when the Fund could invest in types of securities that it is no longer able to hold. Future performance of the Fund may be lower as a result. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. More up-to-date performance information is available at https://​www.massmutual.com/funds or by calling 1-888-309-3539.

Annual Performance

Class R5 Shares

Average Annual Total Returns

(for the periods ended December 31, 2023)

MANAGEMENT

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

Subadviser(s): Barings LLC (“Barings”)

Portfolio Manager(s):

Adam Cash is a Director and portfolio manager for Barings’ Global Public Fixed Income Trading and Trading Solutions Group. He has managed the Fund since May 2022.

Scott Simler is a Director and portfolio manager for Barings’ Global Public Fixed Income Trading and Trading Solutions Group. He has managed the Fund since July 2009.

PURCHASE AND SALE OF FUND SHARES

Shares of the Fund are generally available through various financial intermediaries, such as retirement plan recordkeepers, broker-dealers, financial institutions, and insurance companies, and to other institutional investors and individual retirement accounts. Fund shares are redeemable on any business day by written request, telephone, or internet (available to certain customers).

TAX INFORMATION

The Fund intends to make distributions that may be taxed as ordinary income, qualified dividend income, or capital gains, unless you are an investor eligible for preferential tax treatment.

PAYMENTS TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES

If you purchase the Fund through a broker-dealer or other financial intermediary, the intermediary may receive a one-time or continuing payments from the Fund, MML Advisers or its affiliates, or others for the sale of Fund shares or continuing shareholder services provided by the intermediary. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary to recommend the Fund over another investment. You should contact your intermediary to obtain more information about the compensation it may receive in connection with your investment.