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Summary Prospectus

May 1, 2025

SunAmerica Series Trust

SA Mid Cap Index Portfolio

(Class 1 and Class 3 Shares)

SunAmerica Series Trust’s Statutory Prospectus and Statement of Additional Information, each dated May 1, 2025, as amended and supplemented from time to time, and the most recent shareholder reports are incorporated into and made part of this Summary Prospectus by reference. The Portfolio is offered only to the separate accounts of certain affiliated and unaffiliated life insurance companies and to other mutual funds. This Summary Prospectus is not intended for use by other investors.

Before you invest, you may want to review SunAmerica Series Trust’s Statutory Prospectus, which contains more information about the Portfolio and its risks. You can find the Statutory Prospectus and the above-incorporated information online at https://www.corebridgefinancial.com/getprospectus. You can also get this information at no cost by calling (800) 445-7862 or by sending an e-mail request to fundprospectus@corebridgefinancial.com.

The Securities and Exchange Commission has not approved or disapproved these securities, nor has it determined that this Summary Prospectus is accurate or complete. It is a criminal offense to state otherwise.

Investment Goal

The Portfolio’s investment goal is investment results that correspond with the performance of the S&P MidCap 400® Index.

Fees and Expenses of the Portfolio

This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Portfolio. The table and the example below do not reflect the separate account fees charged in the variable annuity or variable life insurance policy (“Variable Contracts”) in which the Portfolio is offered. If separate account fees were shown, the Portfolio’s annual operating expenses would be higher. Please see your Variable Contract prospectus for more details on the separate account fees.

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

	Class 1	Class 3
Management Fees	0.30%	0.30%
Service (12b-1) Fees	None	0.25%
Other Expenses	0.06%	0.06%
Total Annual Portfolio Operating Expenses	0.36%	0.61%

Expense Example

This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and

then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same (except that the Example incorporates any applicable fee waiver and/or expense limitation arrangements for only the first year). The Example does not reflect charges imposed by the Variable Contract. If the Variable Contract fees were reflected, the expenses would be higher. See the Variable Contract prospectus for information on such charges. Although your actual costs may be higher or lower, based on these assumptions and the net expenses shown in the fee table, your costs would be:

	1 Year	3 Years	5 Years	10 Years
Class 1	$37	$116	$202	$456
Class 3	62	195	340	762

Portfolio Turnover

The Portfolio 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 portfolio operating expenses or in the Example, affect the Portfolio’s performance.

During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 21% of the average value of its portfolio.

Principal Investment Strategies of the Portfolio

The Portfolio seeks to provide investment results that correspond with the performance of the S&P MidCap

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400® Index (the “Index”). The Index is a capitalization-weighted index designed to measure the performance of mid-sized companies in the United States.

The subadviser primarily seeks to achieve the Portfolio’s objective by investing in all or substantially all of the stocks included in the Index, a strategy known as “replication.” The subadviser may, however, utilize an “optimization” strategy in circumstances in which replication is difficult or impossible, such as if the Portfolio has low asset levels and cannot replicate, to reduce trading costs or to gain exposure to securities that the Portfolio cannot access directly. The goal of optimization is to select stocks which ensure that characteristics such as industry weightings, average market capitalizations and fundamental characteristics (e.g., price-to-book, price-to-earnings, debt-to-asset ratios and dividend yields) closely approximate those of the Index. Stocks not in the Index may be held before or after changes in the composition of the Index or if they have characteristics similar to stocks in the Index. Under normal circumstances, the Portfolio invests substantially all, but at least 80%, of its net assets in securities included in the Index or in securities that the subadviser determines have economic characteristics that are comparable to the economic characteristics of securities included in the Index, including derivatives, such as contracts for differences. The Portfolio will not concentrate, except to approximately the same extent as the Index may concentrate, in the securities of any industry. It is not anticipated, however, that the Portfolio will, under normal circumstances, be concentrated in the securities of any industry.

Because the Portfolio will generally not hold all of the stocks included in the Index, and because the Portfolio has expenses and the Index does not, the Portfolio will not duplicate the Index’s performance precisely. However, the subadviser believes there should be a close correlation between the Portfolio’s performance and that of the Index in both rising and falling markets.

Principal Risks of Investing in the Portfolio

As with any mutual fund, there can be no assurance that the Portfolio’s investment goal will be met or that the net return on an investment in the Portfolio will exceed what could have been obtained through other investment or savings vehicles. Shares of the Portfolio are not bank deposits and are not guaranteed or insured by any bank, government entity or the Federal Deposit Insurance Corporation. If the value of the assets of the Portfolio goes down, you could lose money.

The following is a summary of the principal risks of investing in the Portfolio.

Equity Securities Risk. The Portfolio invests principally in equity securities and is therefore subject to the risk that stock prices will fall and may underperform other asset classes. Individual stock prices fluctuate from day-to-day and may decline significantly.

Medium Sized Companies Risk. Securities of medium sized companies are usually more volatile and entail greater risks than securities of large companies.

Real Estate Investment Trusts Risk. REITs are trusts that invest primarily in commercial real estate, residential real estate or real estate related loans. The value of an interest in a REIT may be affected by the value and the cash flows of the properties owned or the quality of the mortgages held by the REIT. The performance of a REIT depends on current economic conditions and the types of real property in which it invests and how well the property is managed. If a REIT concentrates its investments in a geographic region or property type, changes in underlying real estate values may have an exaggerated effect on the value of the REIT.

Failure to Match Index Performance Risk. The ability of the Portfolio to match the performance of the Index may be affected by, among other things, changes in securities markets, the manner in which performance of the Index is calculated, changes in the composition of the Index, the amount and timing of cash flows into and out of the Portfolio, commissions, portfolio expenses, and any differences in the pricing of securities by the Portfolio and the Index. When the Portfolio employs an “optimization” strategy, the Portfolio is subject to an increased risk of tracking error, in that the securities selected in the aggregate for the Portfolio may perform differently than the underlying index.

“Passively Managed” Strategy Risk. The Portfolio will not deviate from its strategy, except to the extent necessary to comply with federal tax laws. If the Portfolio’s strategy is unsuccessful, the Portfolio will not meet its investment goal. Because the Portfolio will not use certain techniques available to other mutual funds to reduce stock market exposure, the Portfolio may be more susceptible to general market declines than other funds.

Issuer Risk. The value of a security may decline for a number of reasons directly related to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods and services.

Market Risk. The Portfolio’s share price or the market as a whole can decline for many reasons or be adversely affected by a number of factors, including, without limitation: weakness in the broad market, a particular

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industry, or specific holdings; adverse political, regulatory or economic developments in the United States or abroad; changes in investor psychology; heavy institutional selling; military confrontations, war, terrorism and other armed conflicts, disease/virus outbreaks and epidemics; recessions; taxation and international tax treaties; currency, interest rate and price fluctuations; and other conditions or events.

Derivatives Risk. A derivative is any financial instrument whose value is based on, and determined by, another security, index, rate or benchmark (i.e., stock options, futures, caps, floors, etc.). To the extent a derivative contract is used to hedge another position in the Portfolio, the Portfolio will be exposed to the risks associated with hedging described below. To the extent an option, futures contract, swap, or other derivative is used to enhance return, rather than as a hedge, the Portfolio will be directly exposed to the risks of the contract. Unfavorable changes in the value of the underlying security, index, rate or benchmark may cause sudden losses. Gains or losses from the Portfolio’s use of derivatives may be substantially greater than the amount of the Portfolio’s investment. Certain derivatives have the potential for undefined loss. Derivatives are also associated with various other risks, including market risk, leverage risk, hedging risk, counterparty risk, valuation risk, regulatory risk, illiquidity risk and interest rate fluctuations risk. The primary risks associated with the Portfolio’s use of derivatives are market risk, counterparty risk and hedging risk.

Affiliated Fund Rebalancing Risk. The Portfolio may be an investment option for other mutual funds for which SunAmerica serves as investment adviser that are managed as “funds of funds.” From time to time, the Portfolio may experience relatively large redemptions or investments due to the rebalancing of a fund of funds. In the event of such redemptions or investments, the Portfolio could be required to sell securities or to invest cash at a time when it is not advantageous to do so.

Performance Information

The following bar chart illustrates the risks of investing in the Portfolio by showing changes in the Portfolio’s performance from calendar year to calendar year and the table compares the Portfolio’s average annual returns to those of the Russell 3000® Index (a broad-based securities market index) and the S&P MidCap 400® Index, which is relevant to the Portfolio because it has characteristics similar to the Portfolio’s investment

strategies. Fees and expenses incurred at the contract level are not reflected in the bar chart or table. If these amounts were reflected, returns would be less than those shown. Of course, past performance is not necessarily an indication of how the Portfolio will perform in the future.

BlackRock Investment Management, LLC assumed subadvisory duties of the Portfolio on April 30, 2025. Prior to April 30, 2025, SunAmerica managed the Portfolio.

(Class 1 Shares)

During the period shown in the bar chart:

Highest Quarterly Return:	December 31, 2020	24.28%
Lowest Quarterly Return:	March 31, 2020	-29.77%
Year to Date Most Recent Quarter:	March 31, 2025	-6.23%

Average Annual Total Returns (For the periods ended December 31, 2024)

	1 Year	5 Years	Since Inception	Inception Date
Class 1 Shares	13.50%	9.88%	9.30%	2/6/2017
Class 3 Shares	13.27%	9.61%	9.03%	2/6/2017
Russell 3000® Index (reflects no deduction for fees, expenses or taxes)	23.81%	13.86%	13.92%
S&P MidCap 400® Index (reflects no deduction for fees, expenses or taxes)	13.93%	10.34%	9.67%

Investment Adviser

The Portfolio’s investment adviser is SunAmerica.

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The Portfolio is subadvised by BlackRock Investment Management, LLC.

Portfolio Managers

Name and Title	Portfolio Manager of the Portfolio Since
Paul Whitehead Managing Director	2025
Jennifer Hsui, CFA Managing Director	2025
Peter Sietsema, CFA Director	2025
Matt Waldron, CFA Managing Director	2025
Steven White Director	2025

Purchases and Sales of Portfolio Shares

Shares of the Portfolios may only be purchased or redeemed through Variable Contracts offered by the separate accounts of participating life insurance companies and by other portfolios of the Trust and Seasons Series Trust. Shares of a Portfolio may be purchased and redeemed each day the New York Stock Exchange is open, at the Portfolio’s net asset value determined after receipt of a request in good order.

The Portfolios do not have any initial or subsequent investment minimums. However, your insurance company may impose investment or account minimums. Please consult the prospectus (or other offering document) for your Variable Contract which may contain additional

information about purchases and redemptions of Portfolio shares.

Tax Information

The Portfolios will not be subject to U.S. federal income tax so long as they qualify as regulated investment companies and distribute their income and gains each year to their shareholders. However, contractholders may be subject to U.S. federal income tax (and a U.S. federal Medicare tax of 3.8% that applies to net investment income, including taxable annuity payments, if applicable) upon withdrawal from a Variable Contract. Contractholders should consult the prospectus (or other offering document) for the Variable Contract for additional information regarding taxation.

Payments to Broker-Dealers and
Other Financial Intermediaries

The Portfolios are not sold directly to the general public but instead are offered as an underlying investment option for Variable Contracts and to other portfolios of the Trust and Seasons Series Trust. A Portfolio and its related companies may make payments to the sponsoring insurance company (or its affiliates) for distribution and/or other services. These payments may create a conflict of interest as they may be a factor that the insurance company considers in including a Portfolio as an underlying investment option in the Variable Contract. The prospectus (or other offering document) for your Variable Contract may contain additional information about these payments.

CSP-86704C_226_234.8 (4/25)

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