Summary Prospectus by Investment Company (Form 497K)

September 30, 2025

SUMMARY PROSPECTUS

SIIT High Yield Bond Fund (SGYAX)

Class A

Before you invest, you may want to review the Fund's Prospectus, which contains information about the Fund and its risks. You can find the Fund's Prospectus and other information about the Fund, including the Fund's Statement of Additional Information and annual and semi-annual reports, online at seic.com/fundprospectuses. You can also get this information at no cost by dialing 1-800-DIAL-SEI. The Fund's Prospectus and Statement of Additional Information, dated September 30, 2025, as may be supplemented from time to time, are incorporated by reference into this Summary Prospectus and may be obtained, free of charge, at the website or phone number noted above.

seic.com

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Investment Goal

Total return.

Fund Fees and Expenses

This table describes the fees and expenses that you may pay if you buy, hold, and sell Fund shares. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in this table and examples below.

ANNUAL FUND OPERATING EXPENSES

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. The Example assumes that you invest $10,000 in the Fund 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 Fund's operating expenses remain the same. 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 and may result in higher taxes when Fund shares are held in a taxable account. 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 53% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the High Yield Bond Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in high yield fixed income securities. The Fund will invest primarily in fixed income securities rated below investment grade (junk bonds), including corporate bonds and debentures, convertible and preferred securities, zero coupon obligations and tranches of collateralized debt obligations (CDOs) and collateralized loan obligations (CLOs).

The Fund uses a multi-manager approach, relying upon a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies to manage portions of the Fund's portfolio under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser). Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. In managing the Fund's assets, the Sub-Advisers and, to the extent applicable, SIMC, seek to select securities that offer a high current yield as well as total return potential. The Fund seeks to have a portfolio of securities that is diversified as to issuers and industries. The Fund's average weighted maturity may vary, but will generally not exceed ten years. There is no limit on the maturity or credit quality of any individual security in which the Fund may invest.

As noted above, the Fund will invest primarily in securities rated BB, B, CCC, CC, C and D. However, it may also invest in non-rated securities or securities rated investment grade (AAA, AA, A and BBB). The Fund may also invest in exchange-traded funds (ETFs) to gain exposure to a particular portion of the market while awaiting an opportunity to purchase securities directly. The Fund may also invest a portion of its assets in bank loans, which are generally non-investment grade (junk bond) floating rate instruments. The Fund may invest in bank loans in the form of participations in the loans (participations) and assignments of all or a portion of the loans from third parties (assignments).

The Fund may also invest in futures contracts, forward contracts and swaps for speculative or hedging purposes. Futures, forwards and swaps are used to synthetically obtain exposure to securities or baskets of securities and to manage the Fund's interest rate duration and yield curve exposure. These derivatives are also used to mitigate the Fund's overall level of risk and/or the Fund's risk to particular types of securities, currencies or market segments. Interest rate swaps are further used to manage the Fund's yield spread sensitivity. When the Fund seeks to take an active long or short position with respect to the likelihood of an event of

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default of a security or basket of securities, the Fund may use credit default swaps. The Fund may buy credit default swaps in an attempt to manage credit risk where the Fund has credit exposure to an issuer and the Fund may sell credit default swaps to more efficiently gain credit exposure to such security or basket of securities.

Principal Risks

Market Risk - The prices of the Fund's fixed income securities respond to economic developments, particularly interest rate changes, as well as to perceptions about the creditworthiness of individual issuers, including governments and their agencies. Generally, the Fund's fixed income securities will decrease in value if interest rates rise and vice versa. In a low interest rate environment, risks associated with rising rates are heightened. Declines in dealer market-making capacity as a result of structural or regulatory changes could decrease liquidity and/or increase volatility in the fixed income markets. Markets for fixed income securities may decline significantly in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value, public perceptions concerning these developments, and adverse investor sentiment or publicity. Similarly, environmental and public health risks, such as natural disasters, epidemics, pandemics or widespread fear that such events may occur, may impact markets adversely and cause market volatility in both the short- and long-term. In response to these events, the Fund's value may fluctuate and/or the Fund may experience increased redemptions from shareholders, which may impact the Fund's liquidity or force the Fund to sell securities into a declining or illiquid market.

Below Investment Grade Securities (Junk Bonds) Risk - Fixed income securities rated below investment grade (junk bonds) involve greater risks of default or downgrade and are generally more volatile than investment grade securities because the prospect for repayment of principal and interest of many of these securities is speculative. Because these securities typically offer a higher rate of return to compensate investors for these risks, they are sometimes referred to as "high yield bonds," but there is no guarantee that an investment in these securities will result in a high rate of return.

Investment Style Risk - The risk that high yield fixed income securities may underperform other segments of the fixed income markets or the fixed income markets as a whole.

Interest Rate Risk - The risk that a change in interest rates will cause a fall in the value of fixed income securities. Generally, the value of the Fund's fixed income securities will vary inversely with the direction of prevailing interest rates. Changing interest rates may have unpredictable effects on the markets and may affect the value and liquidity of instruments held by the Fund. Although U.S. Government securities are considered to be among the safest investments, they are not guaranteed against price movements due to changing interest rates.

Corporate Fixed Income Securities Risk - Corporate fixed income securities respond to economic developments, especially changes in interest rates, as well as perceptions of the creditworthiness and business prospects of individual issuers.

Convertible and Preferred Securities Risk - Convertible and preferred securities have many of the same characteristics as stocks, including many of the same risks. In addition, convertible bonds may be more sensitive to changes in interest rates than stocks. Convertible bonds may also have credit ratings below investment grade, meaning that they carry a higher risk of failure by the issuer to pay principal and/or interest when due.

Investing in Limited Recourse Obligations Risk - Collateralized debt obligation (CDO) and collateralized loan obligation (CLO) securities are non-recourse obligations of their issuer payable solely from the related underlying collateral or its proceeds. Therefore, as a holder of CDOs and CLOs, the Fund must rely only on distributions on the underlying collateral or related proceeds for payment. If distributions on the underlying collateral are insufficient to make payments on the CDO or CLO securities, no other assets will be available for payment of the deficiency. As a result, the amount and timing of interest and principal payments in respect of CDO and CLO securities will depend on the performance and characteristics of the related underlying collateral.

Exchange-Traded Funds Risk - The risks of owning shares of an ETF generally reflect the risks of owning the underlying securities the ETF is designed to track, although lack of liquidity in an ETF could result in its value being more volatile than the underlying portfolio securities. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF's expenses.

Bank Loans Risk - With respect to bank loans, the Fund will assume the credit risk of both the borrower of the loan and the lender that is selling the participation in the loan. The Fund may also have difficulty disposing of bank loans because, in certain cases, the market for such instruments is not highly liquid.

Derivatives Risk - The Fund's use of futures contracts, forwards contracts and swaps is subject to market risk, leverage risk, correlation risk and liquidity risk. Leverage risk and liquidity risk are described below and market risk is described above. Many over-the-counter (OTC) derivative instruments will not have liquidity beyond the counterparty to the instrument. Correlation risk is the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset, rate or index. The Fund's use of forward contracts and swaps is also subject to credit risk and valuation risk. Credit risk is described below. Valuation

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risk is the risk that the derivative may be difficult to value and/or valued incorrectly. Each of these risks could cause the Fund to lose more than the principal amount invested in a derivative instrument. Some derivatives have the potential for unlimited loss, regardless of the size of the Fund's initial investment. The other parties to certain derivative contracts present the same types of credit risk as issuers of fixed income securities. The Fund's use of derivatives may also increase the amount of taxes payable by shareholders. Both U.S. and non-U.S. regulators have adopted and implemented regulations governing derivatives markets, the ultimate impact of which remains unclear.

Credit Risk - The risk that the issuer of a security or the counterparty to a contract will default or otherwise become unable to honor a financial obligation.

Liquidity Risk - The risk that certain securities may be difficult or impossible to sell at the time and the price that the Fund would like. The Fund may have to lower the price of the security, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance.

Duration Risk - The longer-term securities in which the Fund may invest are more volatile. A portfolio with a longer average portfolio duration is more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration.

Extension Risk - The risk that rising interest rates may extend the duration of a fixed income security, typically reducing the security's value.

Prepayment Risk - The risk that, in a declining interest rate environment, fixed income securities with stated interest rates may have the principal paid earlier than expected, requiring the Fund to invest the proceeds at generally lower interest rates.

Leverage Risk - The Fund's use of derivatives may result in the Fund's total investment exposure substantially exceeding the value of its portfolio securities and the Fund's investment returns depending substantially on the performance of securities that the Fund may not directly own. The use of leverage can amplify the effects of market volatility on the Fund's share price and may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations. The Fund's use of leverage may result in a heightened risk of investment loss.

Investing in the Fund involves risk, and there is no guarantee that the Fund will achieve its investment goal. You could lose money on your investment in the Fund, just as you could with other investments. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Performance Information

The bar chart and the performance table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year for the past ten calendar years and by showing how the Fund's average annual returns for 1, 5 and 10 years, and since the Fund's inception compare with those of a broad measure of market performance. The performance information shown is based on full calendar years. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. For current performance information, please call 1-800-DIAL-SEI.

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

This table compares the Fund's average annual total returns to those of a broad-based securities market index and an additional index with characteristics relevant to the Fund's investment strategy.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as

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401(k) plans or individual retirement accounts. In some cases, the Fund's return after taxes may exceed the Fund's return before taxes due to an assumed tax benefit from any losses on a sale of Fund shares at the end of the measurement period.

Management

Investment Adviser and Portfolio Managers. SEI Investments Management Corporation

Sub-Advisers and Portfolio Managers.

Purchase and Sale of Fund Shares

The Fund's minimum investment requirements for Class A Shares are: (a) that you must be an Eligible Investor (i.e., institutions or other SIMC advisory clients that have entered into an investment management agreement with SIMC or institutional investors, employee benefit plans and other similar entities purchasing through approved intermediaries); and (b) that your minimum initial investment must be $100,000, with minimum subsequent investments of $1,000, which may be waived at the discretion of SIMC. You may purchase and redeem shares of the Fund on any day that the New York Stock Exchange (NYSE) is open for business (a Business Day). You may sell your Fund shares by contacting your authorized financial institution or intermediary directly. Authorized financial institutions and intermediaries may redeem Fund shares on behalf of their clients by contacting the Fund's transfer agent (the Transfer Agent) or the Fund's authorized agent, using certain SEI Investments Company (SEI) or third party systems or by calling 1-800-858-7233, as applicable.

Tax Information

The distributions made by the Fund are generally taxable and will be taxed as qualified dividend income, ordinary income or capital gains. If you are investing through a tax-deferred arrangement, such as a 401(k) plan or individual retirement account, you will generally not be subject to federal taxation on Fund distributions until you begin receiving distributions from your tax-deferred arrangement. You should consult your tax advisor regarding the rules governing your tax-deferred arrangement.

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Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase Fund shares through a broker-dealer or other financial intermediary, such as a bank, the Fund and its related companies may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary's website for more information.