Summary Prospectus by Investment Company - Form 497K

Summary Prospectus

May 1, 2024

SunAmerica Series Trust

SA Fixed Income Index Portfolio

(Class 1 and Class 3 Shares)

SunAmerica Series Trust's Statutory Prospectus and Statement of Additional Information, each dated May 1, 2024, 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 [email protected].

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 Bloomberg U.S. Government/Credit 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 Before Fee Waivers and/ or Expense Reimbursements	0.36%	0.61%
Fee Waivers and/or Expense Reimbursements1	0.02%	0.02%
Total Annual Portfolio Operating Expenses After Fee Waivers and/or Expense Reimbursements1	0.34%	0.59%

agreed to waive its fees and/or reimburse expenses to the extent that the Total Annual Portfolio Operating Expenses of Class 1 and Class 3 shares exceed 0.34% and 0.59%, respectively, of the Portfolio's average daily net assets. For purposes of the Expense Limitation Agreement, "Total Annual Portfolio Operating Expenses" shall not include extraordinary expenses (i.e., expenses that are unusual in nature and infrequent in occurrence, such as litigation), or acquired fund fees and expenses, brokerage commissions and other transactional expenses relating to the purchase and sale of portfolio securities, interest, taxes and governmental fees, and other expenses not incurred in the ordinary course of business of SunAmerica Series Trust (the "Trust") on behalf of the Portfolio. Any waivers and/or reimbursements made by SunAmerica with respect to the Portfolio are subject to recoupment from the Portfolio within two years after the occurrence of the waiver and/or reimbursement, provided that the recoupment does not cause the expense ratio of the share class to exceed the lesser of (a) the expense limitation in effect at the time the waivers and/or reimbursements occurred, or (b) the current expense limitation of that share class. This agreement may be modified or discontinued prior to April 30, 2025, only with the approval of the Board of Trustees of the Trust, including a majority of the trustees who are not "interested persons" of the Trust as defined in the Investment Company Act of 1940, as amended.

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 and that all contractual expense limitations and fee waivers remain in effect only for the period ending April 30, 2025. 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	$35	$114	$200	$454
Class 3	60	193	338	760

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 12% 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 Bloomberg U.S. Government/Credit Index (the "Index"). The Index measures the performance of U.S. dollar-denominated U.S. Treasury bonds, government-related bonds and investment-grade U.S. corporate bonds that have a remaining maturity of greater than or equal to one year.

The Adviser may achieve the Portfolio's objective by investing in a sampling of securities included in the Index by utilizing a statistical technique known as "optimization." The goal of optimization is to select securities which ensure that characteristics such as industry weightings, average market capitalizations and fundamental characteristics (e.g., return variability, duration, maturity, credit rating and yield) closely approximate those of the Index. Securities not in the Index may be held before or after changes in the composition of the Index or if they have characteristics similar to securities in the Index. Under normal circumstances, all of the Portfolio's investments will be selected through the optimization process, and at least 80% of its net assets will be invested in securities included in the Index or in securities that SunAmerica, the Portfolio's investment adviser, determines have economic characteristics that are comparable to the economic characteristics of securities included in the Index. 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 securities 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 Adviser 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.

Bonds Risk. The value of your investment in the Portfolio may go up or down in response to changes in interest rates or defaults (or even the potential for future defaults) by bond issuers. Fixed income securities may be subject to volatility due to changes in interest rates.

Credit Risk. Credit risk applies to most fixed income securities, but is generally not a factor for obligations backed by the "full faith and credit" of the U.S. Government. The Portfolio could lose money if the issuer of a fixed income security is unable or perceived to be unable to pay interest or to repay principal when it becomes due.

An issuer with a lower credit rating will be more likely than a higher rated issuer to default or otherwise become unable to honor its financial obligations. Issuers with low credit ratings typically issue junk bonds. In addition to the risk of default, junk bonds may be more volatile, less liquid, more difficult to value and more susceptible to adverse economic conditions or investor perceptions than other bonds.

Interest Rate Risk. Fixed income securities may be subject to volatility due to changes in interest rates. Duration is a measure of interest rate risk that indicates how price-sensitive a bond is to changes in interest rates. Longer-term and lower coupon bonds tend to be more sensitive to changes in interest rates. Any future changes in monetary policy made by central banks and/or their governments are likely to affect the level of interest rates.

U.S. Government Obligations Risk. U.S. Treasury obligations are backed by the "full faith and credit" of the U.S. Government and generally have negligible credit risk.

Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government.

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.

Management Risk. The Portfolio is subject to management risk. The Portfolio's portfolio managers apply investment techniques and risk analyses in making investment decisions, but there can be no guarantee that these decisions or the individual securities selected by the portfolio managers will produce the desired results.

"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 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.

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 Bloomberg U.S. Aggregate Bond Index (a broad-based securities market index) and the Bloomberg U.S. Government/Credit 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.

(Class 1 Shares)

During the period shown in the bar chart:

Highest Quarterly Return:	December 31, 2023	6.26%
Lowest Quarterly Return:	March 31, 2022	-5.74%
Year to Date Most Recent Quarter:	March 31, 2024	-0.63%

Average Annual Total Returns (For the periods ended December 31, 2023)

	1 Year	5 Years	Since Inception	Inception Date
Class 1 Shares	5.80%	1.39%	1.31%	2/6/2017
Class 3 Shares	5.48%	1.13%	1.05%	2/6/2017
Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses or taxes)	5.53%	1.10%	1.31%
Bloomberg U.S. Government/ Credit Index (reflects no deduction for fees, expenses or taxes)	5.72%	1.41%	1.52%

Investment Adviser

The Portfolio's investment adviser is SunAmerica.

Portfolio Managers

Name and Title	Portfolio Manager of the Portfolio Since
Timothy Campion Co-Portfolio Manager	2018
Elizabeth Mauro Co-Portfolio Manager	2019

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.