Sep. 28, 2026 | ||||||||||||||||||||||||||||||||||||||||||||||||
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| SIIT Extended Market Index Fund | EXTENDED MARKET INDEX FUND | ||||||||||||||||||||||||||||||||||||||||||||||||
| Investment Goal | ||||||||||||||||||||||||||||||||||||||||||||||||
Seeks investment results that approximate, as closely as practicable and before expenses, the performance of the Russell Small Cap Completeness 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) | ||||||||||||||||||||||||||||||||||||||||||||||||
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| 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: | ||||||||||||||||||||||||||||||||||||||||||||||||
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| PORTFOLIO TURNOVER | ||||||||||||||||||||||||||||||||||||||||||||||||
The Fund will pay 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 23% of the average value of its portfolio. | ||||||||||||||||||||||||||||||||||||||||||||||||
| Principal Investment Strategies | ||||||||||||||||||||||||||||||||||||||||||||||||
The Fund is managed using a passive/indexing investment approach and invests substantially all of its assets in securities (mostly common stocks) of companies that are included (at the time of purchase) in the Russell Small Cap Completeness Index (the Index). As of July 31, 2026, the market capitalization of the companies included in the Index ranged from $6.99 million to $1.43 trillion. The Index is composed of securities of the companies included in the Russell 3000 Index (which includes the largest 3,000 U.S. companies), excluding the securities of companies that are constituents of the S&P 500 Index (which includes 500 leading U.S. companies). The Index is constructed to attempt to provide a comprehensive and unbiased barometer of the extended broad market of U.S. equity securities beyond that of the 500 leading U.S. companies included in the S&P 500 Index. The Fund’s investment performance will depend on the Fund’s tracking of the Index and the performance of the Index. The market capitalization range and the composition of the Index are subject to change. The Fund may become “non-diversified,” as defined in the Investment Company Act of 1940, 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 Fund generally will attempt to invest in securities (including interests of real estate investment trusts (REITs)) composing the Index in approximately the same proportions as they are represented in the Index. The Fund’s ability to fully 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. In some cases, 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 Fund’s Sub-Adviser may employ a sampling or optimization technique to construct the Fund’s portfolio. In seeking to replicate the performance of the Index, the Fund may also invest in exchange-traded funds (ETFs) and REITs that are not constituents of the Index. The Sub-Adviser may sell an investment if the merit of the investment has been substantially impaired by extraordinary events or adverse financial conditions. The Fund may, at times, purchase or sell index futures contracts, or options on those futures, or engage in forward or swap transactions in lieu of investing directly in the securities making up the Index or to enhance the Fund’s replication of the Index’s return. In addition, for liquidity purposes, the Fund may invest in securities that are not included in the Index, cash and cash equivalents or money market instruments, such as reverse repurchase agreements and money market funds. The Fund’s return may not match the return of the Index. | ||||||||||||||||||||||||||||||||||||||||||||||||
| 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. | ||||||||||||||||||||||||||||||||||||||||||||||||
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Best Quarter: 30.60% (6/30/20) | ||||||||||||||||||||||||||||||||||||||||||||||||
| Average Annual Total Returns (for the periods ended December 31, 2025) | ||||||||||||||||||||||||||||||||||||||||||||||||
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. | ||||||||||||||||||||||||||||||||||||||||||||||||
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