# EDGAR Filing Document

**Accession Number:** 0000939934
**File Stem:** 0001104659-25-113737
**Filing Date:** 2025-11
**Character Count:** 21904
**Document Hash:** 35df8874c41c585445b8224a6fbad4e5
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-113737.hdr.sgml**: 20251118

**ACCESSION NUMBER**: 0001104659-25-113737

**CONFORMED SUBMISSION TYPE**: 497

**PUBLIC DOCUMENT COUNT**: 26

**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:** 497
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 033-58041
- **FILM NUMBER:** 251495872

**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 LONG DURATION FUND (Series ID: S000006762)

---

|  |  |  |
|:---|:---|:---|
| Class Name                        | Ticker Symbol | Class ID   |
| SIIT LONG DURATION FUND - CLASS A | LDRAX         | C000018351 |

---

### SIIT HIGH YIELD BOND FUND (Series ID: S000006763)

---

|  |  |  |
|:---|:---|:---|
| Class Name                          | Ticker Symbol | Class ID   |
| SIIT HIGH YIELD BOND FUND - CLASS A | SGYAX         | C000018352 |

---

### SIIT EMERGING MARKETS DEBT FUND (Series ID: S000006764)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                | Ticker Symbol | Class ID   |
| SIIT EMERGING MARKETS DEBT FUND - CLASS A | SEDAX         | C000018353 |

---

### SIIT WORLD EQUITY EX-US FUND (Series ID: S000006765)

---

|  |  |  |
|:---|:---|:---|
| Class Name                             | Ticker Symbol | Class ID   |
| SIIT WORLD EQUITY EX-US FUND - CLASS A | WEUSX         | C000018354 |

---

### SIIT CORE FIXED INCOME (Series ID: S000006766)

---

|  |  |  |
|:---|:---|:---|
| Class Name                       | Ticker Symbol | Class ID   |
| SIIT CORE FIXED INCOME - CLASS A | SCOAX         | C000018355 |

---

### SIIT LARGE CAP FUND (Series ID: S000006767)

---

|  |  |  |
|:---|:---|:---|
| Class Name                    | Ticker Symbol | Class ID   |
| SIIT LARGE CAP FUND - CLASS A | SLCAX         | C000018356 |

---

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

---

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

---

### SIIT LARGE CAP DISCIPLINED EQUITY FUND (Series ID: S000006769)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                       | Ticker Symbol | Class ID   |
| SIIT LARGE CAP DISCIPLINED EQUITY FUND - CLASS A | SCPAX         | C000018358 |

---

### SIIT SMALL MID CAP EQUITY FUND (Series ID: S000006770)

---

|  |  |  |
|:---|:---|:---|
| Class Name                               | Ticker Symbol | Class ID   |
| SIIT SMALL MID CAP EQUITY FUND - CLASS A | SSMAX         | C000018359 |

---

### SIIT SMALL CAP FUND (Series ID: S000006772)

---

|  |  |  |
|:---|:---|:---|
| Class Name                    | Ticker Symbol | Class ID   |
| SIIT SMALL CAP FUND - CLASS A | SLPAX         | C000018361 |

---

### SIIT EMERGING MARKETS EQUITY FUND (Series ID: S000010881)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                  | Ticker Symbol | Class ID   |
| SIIT EMERGING MARKETS EQUITY FUND - CLASS A | SMQFX         | C000030145 |

---

### SIIT U.S. Managed Volatility Fund (Series ID: S000013605)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                  | Ticker Symbol | Class ID   |
| SIIT U.S. Managed Volatility Fund - Class A | SVYAX         | C000036888 |

---

### SIIT Real Return Fund (Series ID: S000013606)

---

|  |  |  |
|:---|:---|:---|
| Class Name                      | Ticker Symbol | Class ID   |
| SIIT Real Return Fund - Class A | RRPAX         | C000036889 |

---

### SIIT Opportunistic Income Fund (Series ID: S000014581)

---

|  |  |  |
|:---|:---|:---|
| Class Name                               | Ticker Symbol | Class ID   |
| SIIT Opportunistic Income Fund - Class A | ENIAX         | C000039813 |

---

### SIIT Screened World Equity Ex-US Fund (Series ID: S000019597)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                      | Ticker Symbol | Class ID   |
| SIIT Screened World Equity Ex-US Fund - Class A | SSEAX         | C000054521 |

---

### SIIT Dynamic Asset Allocation Fund (Series ID: S000027147)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                   | Ticker Symbol | Class ID   |
| SIIT Dynamic Asset Allocation Fund - Class A | SDLAX         | C000081914 |

---

### SIIT Ultra Short Duration Bond Fund (Series ID: S000031047)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                    | Ticker Symbol | Class ID   |
| SIIT Ultra Short Duration Bond Fund - Class A | SUSAX         | C000096276 |

---

### SIIT Multi-Asset Real Return Fund (Series ID: S000033123)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                  | Ticker Symbol | Class ID   |
| SIIT Multi-Asset Real Return Fund - Class A | SEIAX         | C000102014 |

---

### SIIT Extended Market Index Fund (Series ID: S000035814)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                | Ticker Symbol | Class ID   |
| SIIT Extended Market Index Fund - Class A | SMXAX         | C000109763 |

---

### SIIT Small Cap II Fund (Series ID: S000036633)

---

|  |  |  |
|:---|:---|:---|
| Class Name                       | Ticker Symbol | Class ID   |
| SIIT Small Cap II Fund - Class A | SECAX         | C000111997 |

---

### SIIT Long Duration Credit Fund (Series ID: S000036875)

---

|  |  |  |
|:---|:---|:---|
| Class Name                               | Ticker Symbol | Class ID   |
| SIIT Long Duration Credit Fund - Class A | SLDAX         | C000112815 |

---

### SIIT S&P 500 Index Fund (Series ID: S000043383)

---

|  |  |  |
|:---|:---|:---|
| Class Name                        | Ticker Symbol | Class ID   |
| SIIT S&P 500 Index Fund - Class A | SPINX         | C000134335 |

---

### SIIT Limited Duration Bond Fund (Series ID: S000046099)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                | Ticker Symbol | Class ID   |
| SIIT Limited Duration Bond Fund - Class A | SLDBX         | C000144225 |

---

### SIIT Intermediate Duration Credit Fund (Series ID: S000047944)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                       | Ticker Symbol | Class ID   |
| SIIT Intermediate Duration Credit Fund - Class A | SIDCX         | C000150792 |

---

### SIIT Global Managed Volatility Fund (Series ID: S000050969)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                    | Ticker Symbol | Class ID   |
| SIIT Global Managed Volatility Fund - Class A | SGMAX         | C000160603 |

---

### SIIT U.S. Equity Factor Allocation Fund (Series ID: S000061159)

---

|  |  |  |
|:---|:---|:---|
| Class Name                                        | Ticker Symbol | Class ID   |
| SIIT U.S. Equity Factor Allocation Fund - Class A | SEHAX         | C000198133 |

---

## Series and Classes Contracts Data

### SIIT LONG DURATION FUND (Series ID: S000006762)

| Class ID   | Class Name                        | Ticker Symbol   |
|:---|:---|:---|
| C000018351 | SIIT LONG DURATION FUND - CLASS A | LDRAX           |

### SIIT HIGH YIELD BOND FUND (Series ID: S000006763)

| Class ID   | Class Name                          | Ticker Symbol   |
|:---|:---|:---|
| C000018352 | SIIT HIGH YIELD BOND FUND - CLASS A | SGYAX           |

### SIIT EMERGING MARKETS DEBT FUND (Series ID: S000006764)

| Class ID   | Class Name                                | Ticker Symbol   |
|:---|:---|:---|
| C000018353 | SIIT EMERGING MARKETS DEBT FUND - CLASS A | SEDAX           |

### SIIT WORLD EQUITY EX-US FUND (Series ID: S000006765)

| Class ID   | Class Name                             | Ticker Symbol   |
|:---|:---|:---|
| C000018354 | SIIT WORLD EQUITY EX-US FUND - CLASS A | WEUSX           |

### SIIT CORE FIXED INCOME (Series ID: S000006766)

| Class ID   | Class Name                       | Ticker Symbol   |
|:---|:---|:---|
| C000018355 | SIIT CORE FIXED INCOME - CLASS A | SCOAX           |

### SIIT LARGE CAP FUND (Series ID: S000006767)

| Class ID   | Class Name                    | Ticker Symbol   |
|:---|:---|:---|
| C000018356 | SIIT LARGE CAP FUND - CLASS A | SLCAX           |

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

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

### SIIT LARGE CAP DISCIPLINED EQUITY FUND (Series ID: S000006769)

| Class ID   | Class Name                                       | Ticker Symbol   |
|:---|:---|:---|
| C000018358 | SIIT LARGE CAP DISCIPLINED EQUITY FUND - CLASS A | SCPAX           |

### SIIT SMALL MID CAP EQUITY FUND (Series ID: S000006770)

| Class ID   | Class Name                               | Ticker Symbol   |
|:---|:---|:---|
| C000018359 | SIIT SMALL MID CAP EQUITY FUND - CLASS A | SSMAX           |

### SIIT SMALL CAP FUND (Series ID: S000006772)

| Class ID   | Class Name                    | Ticker Symbol   |
|:---|:---|:---|
| C000018361 | SIIT SMALL CAP FUND - CLASS A | SLPAX           |

### SIIT EMERGING MARKETS EQUITY FUND (Series ID: S000010881)

| Class ID   | Class Name                                  | Ticker Symbol   |
|:---|:---|:---|
| C000030145 | SIIT EMERGING MARKETS EQUITY FUND - CLASS A | SMQFX           |

### SIIT U.S. Managed Volatility Fund (Series ID: S000013605)

| Class ID   | Class Name                                  | Ticker Symbol   |
|:---|:---|:---|
| C000036888 | SIIT U.S. Managed Volatility Fund - Class A | SVYAX           |

### SIIT Real Return Fund (Series ID: S000013606)

| Class ID   | Class Name                      | Ticker Symbol   |
|:---|:---|:---|
| C000036889 | SIIT Real Return Fund - Class A | RRPAX           |

### SIIT Opportunistic Income Fund (Series ID: S000014581)

| Class ID   | Class Name                               | Ticker Symbol   |
|:---|:---|:---|
| C000039813 | SIIT Opportunistic Income Fund - Class A | ENIAX           |

### SIIT Screened World Equity Ex-US Fund (Series ID: S000019597)

| Class ID   | Class Name                                      | Ticker Symbol   |
|:---|:---|:---|
| C000054521 | SIIT Screened World Equity Ex-US Fund - Class A | SSEAX           |

### SIIT Dynamic Asset Allocation Fund (Series ID: S000027147)

| Class ID   | Class Name                                   | Ticker Symbol   |
|:---|:---|:---|
| C000081914 | SIIT Dynamic Asset Allocation Fund - Class A | SDLAX           |

### SIIT Ultra Short Duration Bond Fund (Series ID: S000031047)

| Class ID   | Class Name                                    | Ticker Symbol   |
|:---|:---|:---|
| C000096276 | SIIT Ultra Short Duration Bond Fund - Class A | SUSAX           |

### SIIT Multi-Asset Real Return Fund (Series ID: S000033123)

| Class ID   | Class Name                                  | Ticker Symbol   |
|:---|:---|:---|
| C000102014 | SIIT Multi-Asset Real Return Fund - Class A | SEIAX           |

### SIIT Extended Market Index Fund (Series ID: S000035814)

| Class ID   | Class Name                                | Ticker Symbol   |
|:---|:---|:---|
| C000109763 | SIIT Extended Market Index Fund - Class A | SMXAX           |

### SIIT Small Cap II Fund (Series ID: S000036633)

| Class ID   | Class Name                       | Ticker Symbol   |
|:---|:---|:---|
| C000111997 | SIIT Small Cap II Fund - Class A | SECAX           |

### SIIT Long Duration Credit Fund (Series ID: S000036875)

| Class ID   | Class Name                               | Ticker Symbol   |
|:---|:---|:---|
| C000112815 | SIIT Long Duration Credit Fund - Class A | SLDAX           |

### SIIT S&P 500 Index Fund (Series ID: S000043383)

| Class ID   | Class Name                        | Ticker Symbol   |
|:---|:---|:---|
| C000134335 | SIIT S&P 500 Index Fund - Class A | SPINX           |

### SIIT Limited Duration Bond Fund (Series ID: S000046099)

| Class ID   | Class Name                                | Ticker Symbol   |
|:---|:---|:---|
| C000144225 | SIIT Limited Duration Bond Fund - Class A | SLDBX           |

### SIIT Intermediate Duration Credit Fund (Series ID: S000047944)

| Class ID   | Class Name                                       | Ticker Symbol   |
|:---|:---|:---|
| C000150792 | SIIT Intermediate Duration Credit Fund - Class A | SIDCX           |

### SIIT Global Managed Volatility Fund (Series ID: S000050969)

| Class ID   | Class Name                                    | Ticker Symbol   |
|:---|:---|:---|
| C000160603 | SIIT Global Managed Volatility Fund - Class A | SGMAX           |

### SIIT U.S. Equity Factor Allocation Fund (Series ID: S000061159)

| Class ID   | Class Name                                        | Ticker Symbol   |
|:---|:---|:---|
| C000198133 | SIIT U.S. Equity Factor Allocation Fund - Class A | SEHAX           |

?xml version='1.0' encoding='ASCII'? 25-31421-2.ba

SEI INSTITUTIONAL INVESTMENTS TRUST

Large Cap Index Fund

S&P 500 Index Fund

Extended Market Index Fund

(the "Funds")

Supplement Dated November 18, 2025

to the Class A Shares Prospectus (the "Prospectus") dated September 30, 2025, as amended

November 3, 2025

This Supplement provides new and additional information beyond that contained in the Prospectus and should be read in conjunction with such Prospectus.

Effective immediately, the Funds are modifying their diversification policy under the Investment Company Act of 1940, as amended (the "1940 Act"), to reflect that each Fund intends to be diversified in approximately the same proportion as the Fund's benchmark index is diversified. The Fund may become "non-diversified," as defined in the 1940 Act, as a result of a change in relative market capitalization or index weighting of one or more constituents of the Fund's benchmark index. Shareholder approval will not be sought if the Fund crosses from diversified to non-diversified status under such circumstances.

*The Prospectus is hereby amended and supplemented to reflect the following changes to the Funds.*

Change in Investment Strategies and Principal Risks of the Funds

*In the Fund Summary of the Large Cap Index Fund, S*&*P 500 Index Fund and Extended Market Index Fund, under the sub-heading "Principal Investment Strategies," the following text is hereby added at the end of the first paragraph:*

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.

*In addition, in the Fund Summary of the Large Cap Index Fund, S*&*P 500 Index Fund and Extended Market Index Fund, under the heading titled "Principal Risks," the following text is hereby added after the last risk:*

*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.

*Additionally, in the section titled "More Information About Risks," under the sub-heading "More Information About Principal Risks," the "Non-Diversification" risk is hereby deleted and replaced with the following:*

*Non-Diversification*—The Emerging Markets Debt Fund is non-diversified. Additionally, in seeking to track an index, the Large Cap Index, the S&P 500 Index and the Extended Market Index Funds 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 they are non-diversified, the Funds 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. However, the Funds intend to satisfy the asset diversification requirements for qualifying as a regulated investment company (RIC) under Subchapter M of the Internal Revenue Code of 1986, as amended (the Code).

*There are no other changes to the Prospectus.*

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE

SEI-F-1630 (11/25)

------

SEI INSTITUTIONAL INVESTMENTS TRUST

Large Cap Fund

Large Cap Disciplined Equity Fun

Large Cap Index Fund

S&P 500 Index Fund

Extended Market Index Fund

Small Cap Fund

Small Cap II Fund

Small/Mid Cap Equity Fund

U.S. Equity Factor Allocation Fund

U.S. Managed Volatility Fund

Global Managed Volatility Fund

World Equity Ex-US Fund

Screened World Equity Ex-US Fund

Emerging Markets Equity Fund

Opportunistic Income Fund

Core Fixed Income Fund

High Yield Bond Fund

Long Duration Fund

Long Duration Credit Fund

Ultra Short Duration Bond Fund

Emerging Markets Debt Fund

Real Return Fund

Limited Duration Bond Fund

Intermediate Duration Credit Fund

Dynamic Asset Allocation Fund

Multi-Asset Real Return Fund

(the "Funds")

Supplement Dated November 18, 2025

to the Statement of Additional Information, dated September 30, 2025, as amended November 3, 2025 (the "SAI")

This Supplement provides new and additional information beyond that contained in the SAI and should be read in conjunction with such SAI.

Change in Investment Strategies and Risks of the Large Cap Index, the S&P 500 Index and the Extended Market Index Funds

*Under the section titled "Investment Objectives and Policies," under the headings titled "Large Cap Index Fund," "S*&*P 500 Index Fund," and "Extended Market Index Fund," the following is hereby added to the end of the second paragraph:*

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.

*In addition, in the section titled "Description of Permitted Investments and Risk Factors," the "Non-Diversification" risk is hereby deleted and replaced with the following:*

NON-DIVERSIFICATION—As indicated in the Investment Limitations section, the Emerging Markets Debt Fund is non-diversified. Additionally, in seeking to track an index, the Large Cap Index, the S&P 500 Index and the Extended Market Index Funds 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. Non-diversified Funds 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. The Funds intend to satisfy the diversification requirements necessary to qualify as a RIC under the Code, as described more fully in the "Taxes" section of this SAI.

------

Change in Non-Fundamental Policy of the Funds

*In the section titled "Investment Limitations," under the heading "Non-Fundamental Policies," Non-Fundamental Policy No. 4 is hereby deleted and replaced with the following:*

Each Fund may not:

*4. With respect to 75% of its total assets: (i) purchase the securities of any issuer (except securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities and securities of other investment companies) if, as a result, more than 5% of its total assets would be invested in the securities of such issuer; or (ii) acquire more than 10% of the outstanding voting securities of any one issuer. Based on interpretive guidance from the SEC Staff, each of the Large Cap Index, S*&*P 500 Index and Extended Market Index Funds periodically may be non-diversified as a result of a change in relative market capitalization or index weighting of one or more constituents of its index. The Funds intend to be diversified in approximately the same proportion as each Fund's benchmark index is diversified. This investment limitation does not apply to the Emerging Markets Debt Fund.*

*In addition, in the same section, in the paragraph titled "Diversification," the following text is hereby added as the second-to-last sentence of the paragraph:*

Certain funds that track an index 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. Shareholder approval will not be sought when the fund crosses from diversified to non-diversified status under such circumstances.

*There are no other changes to the SAI.*

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE

SEI-F-1631 (11/25)

------