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Summary Prospectus April 25, 2025

MML Series Investment Fund II

MML Invesco Discovery Mid Cap Fund (Not currently available)

Class II, 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/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 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)

	Class II	Service Class I
Management Fees	0.64%	0.64%
Distribution and Service (Rule 12b-1) Fees	None	0.25%
Other Expenses(1)	0.19%	0.19%
Total Annual Fund Operating Expenses	0.83%	1.08%

(1)

Other expenses are based on estimated amounts for the current fiscal year of the Fund.

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
Class II	$85	$265
Service Class I	$110	$343

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.

INVESTMENTS, RISKS, AND PERFORMANCE

Principal Investment Strategies

The Fund mainly invests in common stocks of U.S. companies that the Fund’s subadviser, Invesco Advisers, Inc. (“Invesco Advisers”), expects to have above-average growth rates. The Fund seeks to invest in newer companies or in more established companies that are in the early growth phase of their business cycle, which is typically marked by above-average growth rates. Under normal circumstances, the Fund invests directly or indirectly at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of mid-cap companies. Equity securities may include common stocks, preferred stocks, securities convertible into common or preferred stock, rights, and warrants. Invesco Advisers currently defines “mid-cap” companies as those that have a market capitalization, at the time of purchase, within the range of market capitalizations of the issuers included in the Russell Midcap® Growth Index during the most recent 11-month period (based on month-end data) plus the most recent data during

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the current month (as of February 28, 2025, between $555.98 million and $82.33 billion). This range is subject to change at any time due to market activity or changes in the composition of that index. The Fund may invest up to 20% of its net assets in companies whose market capitalizations at the time of investment are outside of that capitalization range.

The Fund invests primarily in U.S. companies but may also purchase securities of issuers in any country, including developed countries and emerging markets (i.e., those that are generally in the early stages of their industrial cycle). The Fund has no limits on the amount of its assets that can be invested in foreign securities, but currently does not intend to invest substantially in such securities. Foreign securities are those of issuers that are organized under the laws of a foreign country or that have a substantial portion of their operations or assets in a foreign country or countries, or that derive a substantial portion of their revenue or profits from businesses, investments or sales outside of the United States, or whose “country of risk” is a foreign country as determined by a third-party service provider. 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 selecting investments for the Fund, Invesco Advisers looks for companies with high growth potential using a “bottom-up” stock selection process. The “bottom-up” approach focuses on fundamental analysis of individual issuers before considering the impact of overall economic, market, or industry trends. This approach includes analysis of a company’s financial statements and management structure and consideration of the company’s operations, product development, and its industry position. Invesco Advisers currently focuses on what it believes to be high-growth companies that are characterized by industry leadership, market share growth, high caliber management teams, sustainable competitive advantages, and strong growth themes or new innovative products or services. As reflected in the Fund’s name, Invesco Advisers’ “Discovery” team of portfolio managers seeks to discover such companies early. Invesco Advisers monitors individual issuers for changes in the factors above, which may trigger Invesco Advisers’ decision to sell a security, but does not require its decision to do so. The factors considered by Invesco Advisers may vary in particular cases and may change over time.

The Fund expects that it will engage in active and frequent trading and so will typically have a relatively high portfolio turnover rate.

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

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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. The Fund may invest in foreign securities known as depositary receipts. Investments in depositary receipts are subject to the same risks as direct investment in foreign securities, which include market, political, currency, and regulatory risks.

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.

Frequent Trading/Portfolio Turnover Risk Portfolio turnover generally involves some expense to the Fund. The trading costs associated with portfolio turnover may adversely affect the Fund’s performance.

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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.

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 Fund had not begun operations prior to the date of this Prospectus, and therefore has no performance history. Because the Fund is new, there is no table which shows how the Fund’s returns have deviated from the broad market. Performance history for the Fund, along with the performance of the Russell 3000® Index as a primary index and the Russell Midcap Growth Index as a secondary index, will be available after the Fund has been in operation for one calendar year.

MANAGEMENT

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

Subadviser(s): Invesco Advisers, Inc. (“Invesco Advisers”)

Portfolio Manager(s):

Justin Livengood, CFA is a Portfolio Manager at Invesco Advisers. He has managed the Fund since its inception (April 2025).

Ronald Zibelli, Jr., CFA is a Portfolio Manager at Invesco Advisers. He has managed the Fund since its inception (April 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

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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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