# EDGAR Filing Document

**Accession Number:** 0000939934
**File Stem:** 0001104659-25-113747
**Filing Date:** 2025-11
**Character Count:** 17317
**Document Hash:** 29331f0a0aca991d90bc31ba25b553a5
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-113747.hdr.sgml**: 20251118

**ACCESSION NUMBER**: 0001104659-25-113747

**CONFORMED SUBMISSION TYPE**: 497K

**PUBLIC DOCUMENT COUNT**: 3

**FILED AS OF DATE**: 20251118

**DATE AS OF CHANGE**: 20251118

**EFFECTIVENESS DATE**: 20251118

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** SEI INSTITUTIONAL INVESTMENTS TRUST
- **CENTRAL INDEX KEY:** 0000939934

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** MA
- **FISCAL YEAR END:** 0531

**FILING VALUES:**
- **FORM TYPE:** 497K
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 033-58041
- **FILM NUMBER:** 251495929

**BUSINESS ADDRESS:**
- **STREET 1:** 1 FREEDOM VALLEY DRIVE
- **CITY:** OAK
- **STATE:** PA
- **ZIP:** 19456
- **BUSINESS PHONE:** 610 676-3097

**MAIL ADDRESS:**
- **STREET 1:** 1 FREEDOM VALLEY DRIVE
- **CITY:** OAK
- **STATE:** PA
- **ZIP:** 19456

## Series and Classes Contracts Data

### SIIT LARGE CAP INDEX FUND (Series ID: S000006768)

| Class ID   | Class Name                          | Ticker Symbol   |
|:---|:---|:---|
| C000018357 | SIIT LARGE CAP INDEX FUND - CLASS A | LCIAX           |

![](j25314215_aa001.jpg)

September 30, 2025, as amended November 18, 2025

SUMMARY PROSPECTUS

SIIT Large Cap Index Fund (LCIAX)

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

------

SEI / SUMMARY PROSPECTUS

Investment Goal

Investment results that correspond to the aggregate price and dividend performance of the securities in the Russell 1000 Index.

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

---

| | |
|:---|:---|
| (expenses that you pay each year as a percentage of the value of your investment) | Class A Shares |
| Management Fees | 0.05% |
| Distribution (12b-1) Fees |  |
| Other Expenses | 0.08% |
| Total Annual Fund Operating Expenses | 0.13% |

---

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:

---

| | | | | |
|:---|:---|:---|:---|:---|
| | 1 Year | 3 Years | 5 Years | 10 Years |
| Large Cap Index Fund — Class A Shares | $13 | $42 | $73 | $166 |

---

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 16% of the average value of its portfolio.

Principal Investment Strategies

The Large Cap Index Fund invests substantially all of its assets (at least 80%) in securities listed in the Russell 1000 Index. The Russell 1000 Index (the Index) measures the performance of the large-cap segment of the U.S. equity universe and includes approximately 1000 of the largest securities based on their market capitalization. The Fund's investment performance will depend on the Fund's tracking of the Index and the performance of the Index. The Fund's ability to replicate the performance of the Index will depend to some extent on the size and timing of cash flows into and out of the Fund, as well as on the level of the Fund's expenses. The Fund may become "non-diversified," as defined in the Investment Company Act of 1940 Act, as amended (the "1940 Act"), as a result of a change in relative market capitalization or index weighting of one or more constituents of the Index.

The Fund's sub-adviser (the Sub-Adviser) selects the Fund's securities under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser), but the Sub-Adviser makes no attempt to "manage" the Fund in the traditional sense (i.e., by using economic, market or financial analyses). Instead, the Sub-Adviser generally will attempt to invest in securities composing the Index in approximately the same proportions as they are represented in the Index. It may not be possible or practicable to purchase all of the securities composing the Index or to hold them in the same weightings as they are represented in the Index. In those cases, the Sub-Adviser may employ a sampling or optimization technique to replicate the Index. In seeking to replicate the performance of the Index, the Fund may invest, to a lesser extent, in American Depositary Receipts (ADRs). The Fund may also invest in securities of companies located in developed foreign countries and securities of small capitalization companies. The Sub-Adviser may, but is not required to, sell an investment if the merit of the investment has been substantially impaired by extraordinary events, such as fraud or a material adverse change in an issuer, or adverse financial conditions. The Fund's return may not match the return of the Index. The Index's market capitalization range and the composition of the Index are subject to change.

Principal Risks

*Market Risk* — The risk that the market value of a security may move up and down, sometimes rapidly and unpredictably. Market risk may affect a single issuer, an industry, a sector or the equity market as a whole. Equity markets may decline significantly in

------

SEI / SUMMARY PROSPECTUS

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.

*Large Capitalization Risk* — The risk that larger, more established companies may be unable to respond quickly to new competitive challenges such as changes in technology and consumer tastes. Larger companies also may not be able to attain the high growth rates of successful smaller companies.

*Investment Style Risk* — The risk that its investment approach, which attempts to replicate the performance of the Russell 1000 Index, may underperform other segments of the equity markets or the equity markets as a whole. The Fund is also subject to the risk that large capitalization securities may underperform other segments of the equity markets or the equity markets as a whole.

*Tracking Error Risk* — The risk that the Fund's performance may vary substantially from the performance of the benchmark index it tracks as a result of cash flows, Fund expenses, imperfect correlation between the Fund's investments and the index's components and other factors.

*Sampling Risk* — The Fund may not fully replicate the benchmark index and may hold securities not included in the index. As a result, the Fund may not track the return of its benchmark index as well as it would have if the Fund purchased all of the securities in its benchmark index.

*Depositary Receipts Risk* — Depositary receipts, such as ADRs, are certificates evidencing ownership of shares of a foreign issuer that are issued by depositary banks and generally trade on an established market. Depositary receipts are subject to many of the risks associated with investing directly in foreign securities, including, among other things, political, social and economic developments abroad, currency movements and different legal, regulatory, tax, accounting and audit environments.

*Foreign Investment Risk* — The risk that non-U.S. securities may be subject to additional risks due to, among other things, political, social and economic developments abroad, currency movements, and different legal, regulatory, tax, accounting and audit environments.

*Small Capitalization Risk* — Smaller capitalization companies in which the Fund may invest may be more vulnerable to adverse business or economic events than larger, more established companies. In particular, small capitalization companies may have limited product lines, markets and financial resources and may depend upon a relatively small management group. Therefore, small capitalization stocks may be more volatile than those of larger companies. Small capitalization stocks may be traded over-the-counter (OTC). OTC stocks may trade less frequently and in smaller volume than exchange listed stocks and may have more price volatility than that of exchange-listed stocks.

*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.

*Currency Risk* — As a result of the Fund's investments in securities or other investments denominated in, and/or receiving revenues in, foreign currencies, the Fund will be subject to currency risk. Currency risk is the risk that foreign currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency hedged. In either event, the dollar value of an investment in the Fund would be adversely affected. Currency exchange rates may fluctuate in response to, among other things, changes in interest rates, intervention (or failure to intervene) by U.S. or foreign governments, central banks or supranational entities, or by the imposition of currency controls or other political developments in the United States or abroad.

*Non-Diversification Risk* — In seeking to track the Index, the Fund may become non-diversified as a result of a change in relative market capitalization or index weighting of one or more constituents of the Index. A non-diversified fund generally invests a greater portion of its assets in the securities of one or more issuers and invests overall in a smaller number of issuers than a diversified fund. When it is non-diversified, the Fund may be more sensitive to a single economic, business, political, regulatory, or other occurrences, which may negatively impact the Fund's performance and result in greater fluctuation in the value of the Fund's shares.

*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

------

SEI / SUMMARY PROSPECTUS

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.

---

| | |
|:---|:---|
| ![](j25314215_ba002.jpg)  | Best Quarter: 21.71% (6/30/20)<br>Worst Quarter: -20.19% (3/31/20)<br>The Fund's total return from January 1, 2025 to June 30, 2025 was 6.03%. |

---

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 401(k) plans or individual retirement accounts.

---

| | | | | |
|:---|:---|:---|:---|:---|
| Large Cap Index Fund | 1 Year | 5 Years | 10 Years | Since<br>Inception<br>(4/1/2002) |
| Return Before Taxes | 24.42% | 14.22% | 12.83% | 9.58% |
| Return After Taxes on Distributions | 20.41% | 11.34% | 10.12% | 8.05% |
| Return After Taxes on Distributions and Sale of Fund Shares | 17.07% | 10.85% | 9.81% | 7.76% |
| S&P 500 Index Return (reflects no deduction for fees, expenses or taxes) | 25.02% | 14.53% | 13.10% | 9.54% |
| Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes) | 24.51% | 14.28% | 12.87% | 9.65% |

---

Management

Investment Adviser and Portfolio Managers. SEI Investments Management Corporation

---

| | | |
|:---|:---|:---|
| Portfolio Manager | Experience with the Fund | Title with Adviser |
| Jason Collins | Since 2016 | Portfolio Manager, Head of Sub-Advised Equity |
| David L. Hintz, CFA | Since 2017 | Portfolio Manager |
| Ryan McKeon, CFA | Since 2024 | Senior Analyst |

---

Sub-Adviser and Portfolio Managers.

---

| | | | |
|:---|:---|:---|:---|
| Sub-Adviser | Portfolio Manager | Experience <br>with the Fund | Title with Sub-Adviser |
| SSGA Funds Management, Inc. | Karl Schneider, CAIA<br>Amy Scofield<br>Emiliano Rabinovich, CFA | Since 2005<br>Since 2011<br>Since 2023 | Managing Director, Co-Head of the Systematic <br>Equity Team in the Americas<br>Principal, Portfolio Manager in the Systematic <br>Equity Team<br>Managing Director, Co-Head of the Systematic <br>Equity Team in the Americas |

---

------

SEI / SUMMARY PROSPECTUS

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.

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.

------