VANGUARD INSTITUTIONAL INDEX FUNDS (Form: 485APOS, Received: 07/21/2023 09:03:45)

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A
REGISTRATION STATEMENT
(NO. 33-34494)

UNDER THE SECURITIES ACT OF 1933

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Post-Effective Amendment No.

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Post-Effective Amendment No. 80

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and

REGISTRATION STATEMENT
(NO. 811-06093)

UNDER THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 81

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VANGUARD INSTITUTIONAL INDEX FUNDS

(Exact Name of Registrant as Specified in Declaration of Trust)

P.O. Box 2600, Valley Forge, PA 19482
(Address of Principal Executive Office)
Registrant’s Telephone Number (610) 669-1000

Anne E. Robinson, Esquire
P.O. Box 876
Valley Forge, PA 19482

It is proposed that this filing will become effective (check appropriate box)

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immediately upon filing pursuant to paragraph (b)

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on [date], pursuant to paragraph (b)

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60 days after filing pursuant to paragraph (a)(1)

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on (date) pursuant to paragraph (a)(1)

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75 days after filing pursuant to paragraph (a)(2)

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on October 20, 2023 pursuant to paragraph (a)(2) of rule 485. If appropriate, check the following box:

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This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Vanguard Extended Market Index Fund

Prospectus

XX, 2023

Investor Shares

Vanguard Extended Market Index Fund Investor Shares (VEXMX)

Subject to Completion
Preliminary Prospectus
Dated July 21, 2023

Information contained in this prospectus is subject to completion or amendment. A registration statement for Vanguard Extended Market Index Fund has been filed with the U.S. Securities and Exchange Commission but has not yet become effective.

Shares of Vanguard Extended Market Index Fund may not be sold, nor may offers to buy be accepted, prior to completion of the reorganization referenced in this Prospectus. This communication shall not constitute an offer to sell, nor shall there be any sale of these securities in any state in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

This prospectus contains financial data for the predecessor fund through the fiscal period ended xx, 2023.

The Securities and Exchange Commission (SEC) has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Contents

Fund Summary	1
Investing in Index Funds	6
More on the Fund	7
The Fund and Vanguard	14
Investment Advisor	15
Dividends, Capital Gains, and Taxes	17
Share Price	20
Financial Highlights	22

Investing With Vanguard	23
Purchasing Shares	23
Converting Shares	26
Redeeming Shares	28
Exchanging Shares	32
Frequent-Trading Limitations	33
Other Rules You Should Know	35
Fund and Account Updates	39
Employer-Sponsored Plans	40
Contacting Vanguard	42
Additional Information	43
Glossary of Investment Terms	45

Fund Summary

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of small- and mid-capitalization stocks.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy, hold, and sell Investor Shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.

Shareholder Fees
(Fees paid directly from your investment)


Sales Charge (Load) Imposed on Purchases	None
Purchase Fee	None
Sales Charge (Load) Imposed on Reinvested Dividends	None
Redemption Fee	None
Account Service Fee Per Year (for certain fund account balances below $5,000,000)	$25

Annual Fund Operating Expenses
(Expenses that you pay each year as a percentage of the value of your investment)


Management Fees	[ ] %
12b-1 Distribution Fee	None
Other Expenses	[ ] %
Total Annual Fund Operating Expenses	[ ] %

Example

The following example is intended to help you compare the cost of investing in the Fund’s Investor Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you were to redeem your investment at the end of the given period. 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
[ ]	[ ]	[ ]	[ ]

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 more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense example, reduce the Fund's performance. During the most recent fiscal period ended xx, 2023, the predecessor fund's portfolio turnover rate was xx% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the Standard & Poor‘s Completion Index, a broadly diversified index of stocks of small and mid-size U.S. companies. The S&P Completion Index contains all of the U.S. common stocks regularly traded on the New York Stock Exchange, Cboe, and the Nasdaq over-the-counter market, except those stocks included in the S&P 500 Index. The Fund invests by sampling the Index, meaning that it holds a broadly diversified collection of securities that, in the aggregate, approximates the full Index in terms of key characteristics. These characteristics include industry weightings and market capitalization, as well as certain financial measures, such as price/earnings ratio and dividend yield.

Principal Risks

An investment in the Fund could lose money over short or long periods of time. You should expect the Fund's share price and total return to fluctuate within a wide range. The Fund is subject to the following risks, which could affect the Fund's performance:

• Stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund’s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund’s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

• Investment style risk, which is the chance that returns from small- and mid- capitalization stocks will trail returns from the overall stock market. Historically, small- and mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. The stock prices of small and mid-size companies tend to experience greater volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

• Index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund’s target index. Index sampling risk for the Fund is expected to be low.

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.

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. Performance shown below prior to XX, 2023, is that of Vanguard Extended Market Index Fund, a series of Vanguard Index Funds (the predecessor fund), which was reorganized into the Fund at the close of business on XX, 2023 (the reorganization). The predecessor fund was managed using the same investment policies, objectives, guidelines, and restrictions as those of the Fund. Prior to the reorganization, the Fund had not yet commenced operations. The bar chart shows how the performance of the Fund‘s Investor Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Investor Shares compare with those of the Fund's target index and another comparative index, which have investment characteristics similar to those of the Fund. Keep in mind that the

Fund's (and the predecessor fund's) past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard Extended Market Index Fund Investor Shares1

[To be updated]

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2023, was xx%.

During the periods shown in the bar chart, the highest and lowest returns for a calendar quarter were:

	Total Return	Quarter
Highest	[ ]
Lowest	[ ]

Average Annual Total Returns for Periods Ended December 31, 2022

	1 Year	5 Years	10 Years
Vanguard Extended Market Index Fund Investor Shares
Return Before Taxes	[ ]	[ ]	[ ]
Return After Taxes on Distributions	[ ]	[ ]	[ ]
Return After Taxes on Distributions and Sale of Fund Shares	[ ]	[ ]	[ ]
Standard & Poor's Completion Index (reflects no deduction for fees, expenses, or taxes)	[ ]	[ ]	[ ]
Dow Jones U.S. Total Stock Market Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)	[ ]	[ ]	[ ]

Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.

Investment Advisor

The Vanguard Group, Inc. (Vanguard)

Portfolio Managers

Donald M. Butler, CFA, Principal of Vanguard. He has co-managed the Fund since its inception in XX 2023 and managed the predecessor fund since 1997 (co-managed since 2016).

Michelle Louie, CFA, Portfolio Manager at Vanguard. She has co-managed the Fund since its inception in XX 2023 and the predecessor fund since February 2023.

Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 982901, El Paso, TX 79998-2901), or by telephone (800-662-2739). Investor Shares are generally available only to Vanguard funds that operate as funds of funds and to certain retirement plan clients that receive recordkeeping services from Vanguard. Financial intermediaries, institutional clients, and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Investor Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

Investing in Index Funds

What Is Indexing?

Indexing is an investment strategy for tracking the performance of a specified market benchmark, or “index.” An index is a group of securities whose overall performance is used as a standard to measure the investment performance of a particular market. There are many types of indexes. Some represent entire markets—such as the U.S. stock market or the U.S. bond market. Other indexes cover market segments—such as small-capitalization stocks or short-term bonds. One cannot invest directly in an index.

The index sponsor determines the securities to include in the index and the weighting of each security in the index. Under normal circumstances, the index sponsor will rebalance an index on a regular schedule. An index sponsor may carry out additional ad hoc index rebalances or delay or cancel a scheduled rebalance. Generally, the index sponsor does not provide any warranty, or accept any liability, with respect to the quality, accuracy, or completeness of either the target index or its related data. Errors made by the index sponsor may occur from time to time and may not be identified by the index sponsor for a period of time or at all. Vanguard does not provide any warranty or guarantee against such errors. Therefore, the gains, losses, or costs associated with the index sponsor’s errors will generally be borne by the index fund and its shareholders.

An index fund seeks to hold all, or a representative sample, of the securities that make up its target index. Index funds attempt to mirror the performance of the target index, for better or worse. However, an index fund generally does not perform exactly like its target index. For example, index funds have operating expenses and transaction costs. Market indexes do not, and therefore they will usually have a slight performance advantage over funds that track them. The ability of an index fund to match its performance to that of its target index can also be impacted by, among other things, the timing and size of cash flows, asset valuation differences, and the size of the fund. Market disruptions could also have an adverse effect on a fund’s ability to adjust its exposure to the required levels in order to track the index. The risk that a fund may not track the performance of its target index may be heightened during times of increased market volatility or other unusual market conditions.

Index funds typically have the following characteristics:

• Variety of investments. Depending on a fund’s benchmark index, the fund may invest in the securities of a variety of companies, industries, and/or governments or government agencies.

• Relative performance consistency. Because they seek to track market benchmarks, index funds usually do not perform dramatically better or worse than their benchmarks.

• Low cost. Index funds are generally inexpensive to run compared with actively managed funds. They have low or no research costs and typically keep trading activity—and thus brokerage commissions and other transaction costs—to a minimum compared with actively managed funds.

More on the Fund

This prospectus describes the principal risks you would face as a Fund shareholder. It is important to keep in mind one of the main principles of investing: generally, the higher the risk of losing money, the higher the potential reward. The reverse, also, is generally true: the lower the risk, the lower the potential reward. As you consider an investment in any mutual fund, you should take into account your personal tolerance for fluctuations in the securities markets. Look for this

symbol throughout the prospectus. It is used to mark detailed information about the more significant risks that you would confront as a Fund shareholder. To highlight terms and concepts important to mutual fund investors, we have provided Plain Talk® explanations along the way. Reading the prospectus will help you decide whether the Fund is the right investment for you. We suggest that you keep this prospectus for future reference.

Prior to XX, 2023, Vanguard Extended Market Index Fund was a series of Vanguard Index Funds (the predecessor fund). Effective at the close of business on XX, 2023, the predecessor fund reorganized into the Fund. Upon completion of the reorganization, the Fund assumed the performance, financial, and other historical information of the predecessor fund. All historical financial information and other information contained in this prospectus relating to Vanguard Extended Market Index Fund for periods prior to the closing of the reorganization is that of the predecessor fund.

Share Class Overview

This prospectus offers the Fund's Investor Shares. Separate prospectuses offer the Fund's Admiral™ Shares, which generally have an investment minimum of $3,000, and Institutional Shares and Institutional Plus Shares, which are generally for investors who invest a minimum of $5 million and $100 million, respectively. Another prospectus offers Institutional Select Shares, which are generally for investors who invest a minimum of $3 billion. In addition, the Fund issues ETF Shares (an exchange-traded class of shares), which are also offered through a separate prospectus.

All share classes offered by the Fund have the same investment objective, strategies, and policies. However, different share classes have different expenses; as a result, their investment returns will differ.

Plain Talk About Fund Expenses

All mutual funds have operating expenses. These expenses, which are

deducted from a fund’s gross income, are expressed as a percentage of the

net assets of the fund. Assuming that operating expenses remain as stated

in the Fees and Expenses section, Vanguard Extended Market Index Fund

Investor Shares' expense ratio would be: 0.xx%, or $x.x0 per $1,000 of

average net assets.

Plain Talk About Costs of Investing

Costs are an important consideration in choosing a mutual fund. That is

because you, as a shareholder, pay a proportionate share of the costs of

operating a fund and any transaction costs incurred when the fund buys or

sells securities. These costs can erode a substantial portion of the gross

income or the capital appreciation a fund achieves. Even seemingly small

differences in expenses can, over time, have a dramatic effect on a

fund’s performance.

The following sections explain the principal investment strategies and policies that the Fund uses in pursuit of its investment objective. The Fund's board of trustees, which oversees the Fund's management, may change investment strategies or policies in the interest of shareholders without a shareholder vote, unless those strategies or policies are designated as fundamental. Under normal circumstances, the Fund will invest at least 80% of its assets in the stocks that make up its target index. The Fund may change its 80% policy only upon 60 days‘ notice to shareholders.

Market Exposure

The Fund is subject to stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund‘s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund's target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

Stocks of publicly traded companies are often classified according to market capitalization, which is the market value of a company's outstanding shares. These classifications typically include small-cap, mid-cap, and large-cap. It is important to understand that there are no “official” definitions of small-, mid-, and large-cap, even among Vanguard fund advisors, and that market capitalization ranges can change over time. The asset-weighted median market capitalization of the predecessor fund's stock holdings as of xx, 2023, was $x.x billion.

The Fund is subject to investment style risk, which is the chance that returns from the types of stocks in which the Fund invests will trail returns from the overall stock market. Historically, small- and mid-capitalization stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. The stock prices of small and mid-size companies tend to experience greater volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

Market disruptions can adversely affect local and global markets as well as normal market conditions and operations. Any such disruptions could have an adverse impact on the value of the Fund's investments and Fund performance.

Security Selection

The Fund attempts to track the investment performance of a benchmark index that measures the return of a particular market segment. The Fund uses a sampling method of indexing, meaning that the Fund’s advisor, using computer programs, generally selects from the target index a representative sample of securities that will resemble the target index in terms of key risk factors and other characteristics. These include industry weightings, market capitalization, and other financial characteristics of stocks.

The Fund is subject to index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund's target index. Index sampling risk for the Fund is expected to be low.

The ability of the advisor to purchase or dispose of certain Fund investments is or may be restricted or impaired because of limitations imposed by law, regulation, or by certain regulators or issuers. As a result, the advisor may be required to limit purchases or sell existing investments. If the Fund is required to limit its investment in a particular issuer, then the Fund may seek to obtain regulatory relief or ownership waivers. Other options the Fund may pursue include seeking to obtain economic exposure to that issuer through alternative means, such as through a derivative or through investment in a wholly owned subsidiary, both of which may be more costly than owning securities of the issuer directly. Ownership restrictions and limitations could result in unanticipated tax consequences to the Fund that may affect the amount, timing, and character of distributions to shareholders. See Other Investment Policies and Risks for further information related to derivatives.

Other Investment Policies and Risks

The Fund reserves the right to substitute a different index for the index it currently tracks if the current index is discontinued, if the Fund's agreement with the sponsor of its target index is terminated, or for any other reason determined in good faith by the Fund’s board of trustees. In any such instance, the substitute index would represent the same market segment as the current index.

The Fund may invest in foreign securities to the extent necessary to carry out its investment strategy of holding all, substantially all, or a representative sample of the stocks that make up the index it tracks. It is not expected that the Fund will invest more than 5% of its assets in foreign securities.

The Fund may also use derivatives such as total return swaps to obtain exposure to a stock, a basket of stocks, or an index. Generally speaking, a derivative is a financial contract whose value is based on the value of a financial asset (such as a stock, a bond, or a currency), a physical asset (such as gold, oil, or wheat), a market index, or a reference rate. Investments in derivatives may subject the Fund to risks different from, and possibly greater than, those of investments directly in the underlying securities or assets. The Fund will not use derivatives for speculation or for the purpose of leveraging (magnifying) investment returns.

Cash Management

The Fund's daily cash balance may be invested in Vanguard Market Liquidity Fund and/or Vanguard Municipal Cash Management Fund (each, a CMT Fund), which are low-cost money market funds. When investing in a CMT Fund, the Fund bears its proportionate share of the expenses of the CMT Fund in which it invests. Vanguard receives no additional revenue from Fund assets invested in a CMT Fund.

Redemption Requests

Methods used to meet redemption requests. Under normal circumstances, the Fund typically expects to meet redemptions with positive cash flows. When this is not an option, the Fund seeks to maintain its risk exposure by selling a cross section of the Fund’s holdings to meet redemptions, while also factoring in transaction costs. Additionally, the Fund may work with larger clients to implement their redemptions in a manner that is least disruptive to the portfolio; see “Potentially disruptive redemptions” under Redeeming Shares in the Investing With Vanguard section.

Under certain circumstances, including under stressed market conditions, there are additional tools that the Fund may use in order to meet redemptions, including advancing the settlement of market trades with counterparties to match investor redemption payments or delaying settlement of an investor’s transaction to match trade settlement within regulatory requirements. The Fund may also suspend payment of redemption proceeds for up to seven days; see “Emergency circumstances” under Redeeming Shares in the Investing With Vanguard section. Additionally under these unusual circumstances, the Fund may borrow money (subject to certain regulatory conditions and if available under board-approved procedures) through an interfund lending facility; through a bank line-of-credit, including a joint committed credit facility; or through an uncommitted line-of-credit from Vanguard in order to meet redemption requests.

of the Fund. Large redemptions may cause the Fund to sell portfolio securities at times when it would not otherwise do so. This may result in the Fund distributing capital gains or other taxable income to non-redeeming shareholders. Large redemptions may also increase the Fund's transaction costs. Redemption activity can occur for many reasons, including shareholder reactions to market movements or other events unrelated to Vanguard’s actions, or when Vanguard makes product changes that, for example, may result in a shareholder redeeming shares of the Fund to purchase shares of another similar fund or investment vehicle. When experiencing large redemptions, the Fund reserves the right to pay all or part of the redemption in-kind and/or delay payment of the redemption proceeds for up to seven calendar days; see “Potentially disruptive redemptions” under Redeeming Shares in the Investing With Vanguard section.

Temporary Investment Measures

The Fund may temporarily depart from its normal investment policies and strategies when the advisor believes that doing so is in the Fund's best interest, so long as the strategy or policy employed is consistent with the Fund's investment objective. For instance, the Fund may invest beyond its normal limits in derivatives or exchange-traded funds that are consistent with the Fund's investment objective when those instruments are more favorably priced or provide needed liquidity, as might be the case when the Fund receives large cash flows that it cannot prudently invest immediately.

Frequent Trading or Market-Timing

Background. Some investors try to profit from strategies involving frequent trading of mutual fund shares, such as market-timing. For funds holding foreign securities, investors may try to take advantage of an anticipated difference between the price of the fund’s shares and price movements in overseas markets, a practice also known as time-zone arbitrage. Investors also may try to engage in frequent trading of funds holding investments such as small-cap stocks and high-yield bonds. As money is shifted into and out of a fund by a shareholder engaging in frequent trading, the fund incurs costs for buying and selling securities, resulting in increased brokerage and administrative costs. These costs are borne by all fund shareholders, including the long-term investors who do not generate the costs. In addition, frequent trading may interfere with an advisor’s ability to efficiently manage the fund.

market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) has adopted policies and procedures reasonably designed to detect and discourage frequent trading and, in some cases, to compensate the fund for the costs associated with it. These policies and procedures do not apply to ETF Shares because frequent trading in ETF Shares generally does not disrupt portfolio management or otherwise harm fund shareholders. Although there is no assurance that Vanguard will be able to detect or prevent frequent trading or market-timing in all circumstances, the following policies have been adopted to address these issues:

• Each Vanguard fund reserves the right to reject any purchase request—including exchanges from other Vanguard funds—without notice and regardless of size. For example, a purchase request could be rejected because the investor has a history of frequent trading or if Vanguard determines that such purchase may negatively affect a fund’s operation or performance.

• Each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) generally prohibits, except as otherwise noted in the Investing With Vanguard section, an investor’s purchases or exchanges into a fund account for 30 calendar days after the investor has redeemed or exchanged out of that fund account.

• Certain Vanguard funds charge shareholders purchase and/or redemption fees on transactions.

See the Investing With Vanguard section of this prospectus for further details on Vanguard’s transaction policies.

The Vanguard fund (other than retail and government money market funds), in determining its net asset value, will use fair-value pricing when appropriate, as described in the Share Price section. Fair-value pricing may reduce or eliminate the profitability of certain frequent-trading strategies.

Do not invest with Vanguard if you are a market-timer.

A precautionary note to investment companies: The Fund's shares are issued by registered investment companies, and therefore the acquisition of such shares by other investment companies and private funds is subject to the restrictions of Section 12(d)(1) of the Investment Company Act of 1940 (the 1940 Act). SEC Rule 12d1-4 under the 1940 Act permits registered investment companies to invest in other registered investment companies beyond the limits in Section 12(d)(1), subject to certain conditions, including that funds with different investment advisors must enter into a fund of funds investment agreement.

Turnover Rate

Although the Fund generally seeks to invest for the long term, the Fund may sell securities regardless of how long they have been held. Generally, an index fund sells securities in response to redemption requests from shareholders of conventional (i.e., not exchange-traded) shares or to changes in the composition of its target index. Turnover rates for mid-cap and small-cap stock index funds tend to be higher than for large-cap stock index funds (although still relatively low, compared with actively managed stock funds) because the indexes they track are more likely to change as a result of companies merging, growing, or failing. The Financial Highlights section of this prospectus shows historical turnover rates for the predecessor fund. A turnover rate of 100%, for example, would mean that the Fund had sold and replaced securities valued at 100% of its net assets within a one-year period. In general, the greater the turnover rate, the greater the impact transaction costs will have on a fund’s return. Also, funds with high turnover rates may be more likely to generate capital gains, including short-term capital gains, that must be distributed to shareholders and will be taxable to shareholders investing through a taxable account.

The Fund and Vanguard

The Fund is a member of The Vanguard Group, Inc. (Vanguard), a family of over 200 funds. All of the funds that are members of Vanguard (other than funds of funds) share in the expenses associated with administrative services and business operations, such as personnel, office space, and equipment.

Vanguard Marketing Corporation provides marketing services to the funds. Although fund shareholders do not pay sales commissions or 12b-1 distribution fees, each fund (other than a fund of funds) or each share class of a fund (in the case of a fund with multiple share classes) pays its allocated share of the Vanguard funds’ marketing costs.

Plain Talk About Vanguard’s Unique Corporate Structure

Vanguard is owned jointly by the funds it oversees and thus indirectly by the

shareholders in those funds. Most other mutual funds are operated by

management companies that are owned by third parties—either public or

private stockholders—and not by the funds they serve.

Investment Advisor

The Vanguard Group, Inc., P.O. Box 2600, Valley Forge, PA 19482, which began operations in 1975, serves as advisor to the Fund through its Equity Index Group. As of XX, 2023, Vanguard served as advisor for approximately $XX trillion in assets. Vanguard provides investment advisory services to the Fund pursuant to the Funds’ Service Agreement and subject to the supervision and oversight of the trustees and officers of the Fund.

For the fiscal period ended XX, 2023, the advisory expenses represented an effective annual rate of less than X.XX% of the predecessor fund’s average net assets. The Fund did not commence operations until XX, 2023.

Under the terms of an SEC exemption, the Fund's board of trustees may, without prior approval from shareholders, change the terms of an advisory agreement with a third-party investment advisor or hire a new third-party investment advisor—either as a replacement for an existing advisor or as an additional advisor. Any significant change in a Fund’s advisory arrangements will be communicated to shareholders in writing. As the Fund's sponsor and overall manager, Vanguard may provide investment advisory services to the Fund at any time. Vanguard may also recommend to the board of trustees that an advisor be hired, terminated, or replaced or that the terms of an existing advisory agreement be revised. The Fund has filed an application seeking a similar SEC exemption with respect to investment advisors that are wholly owned subsidiaries of Vanguard. If the exemption is granted, the Fund may rely on the new SEC relief.

For a discussion of why the board of trustees approved the Fund's investment advisory arrangement, see the Fund’s first annual or semiannual report to shareholders following the Fund’s commencement of operations.

The managers primarily responsible for the day-to-day management of the Fund are:

its inception in XX 2023 and the predecessor fund since February 2023. Education: B.S., The American University; M.B.A., Georgia Institute of Technology.

The Fund's Statement of Additional Information provides information about the portfolio manager’s compensation, other accounts under management, and ownership of shares of the Fund.

Dividends, Capital Gains, and Taxes

Fund Distributions

The Fund distributes to shareholders virtually all of its net income (interest and dividends, less expenses) as well as any net short-term or long-term capital gains realized from the sale of its holdings. From time to time, the Fund may also make distributions that are treated as a return of capital. Income dividends generally are distributed quarterly in March, June, September, and December; capital gains distributions, if any, generally occur annually in December. In addition, the Fund may occasionally make a supplemental distribution at some other time during the year.
You can receive distributions of income or capital gains in cash, or you can have them automatically reinvested in more shares of the Fund. However, if you are investing through an employer-sponsored retirement or savings plan, your distributions will be automatically reinvested in additional Fund shares.

Plain Talk About Distributions

As a shareholder, you are entitled to your portion of a fund’s income from

interest as well as capital gains from the fund’s sale of investments. Income

consists of interest the fund earns from its money market and bond

investments. Income consists of both the dividends that the fund earns from

any stock holdings and the interest it receives from any money market and

bond investments. Capital gains are realized whenever the fund sells

securities for higher prices than it paid for them. These capital gains are

either short-term or long-term, depending on whether the fund held the

securities for one year or less or for more than one year.

Basic Tax Points

Investors in taxable accounts should be aware of the following basic federal income tax points:

• Distributions are taxable to you whether or not you reinvest these amounts in additional Fund shares.

• Distributions declared in December—if paid to you by the end of January—are taxable as if received in December.

be eligible for reduced tax rates on “qualified dividend income,” if any, or a special tax deduction on “qualified REIT dividends,” if any, distributed by the Fund.

• Any distribution of net long-term capital gains is taxable to you as long-term capital gains, no matter how long you have owned shares in the Fund.

• Capital gains distributions may vary considerably from year to year as a result of the Fund's normal investment activities and cash flows.

• Your cost basis in the Fund will be decreased by the amount of any return of capital that you receive. This, in turn, will affect the amount of any capital gain or loss that you realize when selling or exchanging your Fund shares.

• Return of capital distributions generally are not taxable to you until your cost basis has been reduced to zero. If your cost basis is at zero, return of capital distributions will be treated as capital gains.

• A sale or exchange of Fund shares is a taxable event. This means that you may have a capital gain to report as income, or a capital loss to report as a deduction, when you complete your tax return.

• Any conversion between classes of shares of the same fund is a nontaxable event. By contrast, an exchange between classes of shares of different funds is a taxable event.

• Vanguard (or your intermediary) will send you a statement each year showing the tax status of all of your distributions.

Individuals, trusts, and estates whose income exceeds certain threshold amounts are subject to a 3.8% Medicare contribution tax on “net investment income.” Net investment income takes into account distributions paid by the Fund and capital gains from any sale or exchange of Fund shares.

Dividend distributions and capital gains distributions that you receive, as well as your gains or losses from any sale or exchange of Fund shares, may be subject to state and local income taxes.

This prospectus provides general tax information only. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply. Please consult your tax advisor for detailed information about any tax consequences for you.

Plain Talk About Buying a Dividend

Unless you are a tax-exempt investor or investing through a tax-advantaged

account (such as an IRA or an employer-sponsored retirement or savings

plan), you should consider avoiding a purchase of fund shares shortly before

the fund makes a distribution, because doing so can cost you money in

taxes. This is known as “buying a dividend.” For example: On December 15,

you invest $5,000, buying 250 shares for $20 each. If the fund pays a

distribution of $1 per share on December 16, its share price will drop to $19

(not counting market change). You still have only $5,000 (250 shares x $19 =

$4,750 in share value, plus 250 shares x $1 = $250 in distributions), but you

owe tax on the $250 distribution you received—even if you reinvest it in

more shares. To avoid buying a dividend, check a fund’s distribution schedule

before you invest.

General Information

Backup withholding. By law, Vanguard must withhold 24% of any taxable distributions or redemptions from your account if you do not:

• Provide your correct taxpayer identification number.

• Certify that the taxpayer identification number is correct.

• Confirm that you are not subject to backup withholding.

Similarly, Vanguard (or your intermediary) must withhold taxes from your account if the IRS instructs us to do so.

Foreign investors. Vanguard funds offered for sale in the United States (Vanguard U.S. funds), including the Fund offered in this prospectus, are not widely available outside the United States. Non-U.S. investors should be aware that U.S. withholding and estate taxes and certain U.S. tax reporting requirements may apply to any investments in Vanguard U.S. funds. Foreign investors should visit the non-U.S. investors page on our website at vanguard.com for information on Vanguard’s non-U.S. products.

Invalid addresses. If a dividend distribution or capital gains distribution check mailed to your address of record is returned as undeliverable, Vanguard will automatically reinvest the distribution and all future distributions until you provide us with a valid mailing address. Reinvestments will receive the net asset value calculated on the date of the reinvestment.

Share Price

Share price, also known as net asset value (NAV), is calculated as of the close of regular trading on the New York Stock Exchange (NYSE), generally 4 p.m., Eastern time, on each day that the NYSE is open for business (a business day). In the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. Each share class has its own NAV, which is computed by dividing the total assets, minus liabilities, allocated to the share class by the number of Fund shares outstanding for that class. On U.S. holidays or other days when the NYSE is closed, the NAV is not calculated, and the Fund does not sell or redeem shares. However, on those days the value of a Fund’s assets may be affected to the extent that the Fund holds securities that change in value on those days (such as foreign securities that trade on foreign markets that are open).

Stocks held by a Vanguard fund are valued at their market value when reliable market quotations are readily available from the principal exchange or market on which they are traded. Such securities are generally valued at their official closing price, the last reported sales price, or if there were no sales that day, the mean between the closing bid and asking prices. When a fund determines that market quotations either are not readily available or do not accurately reflect the value of a security, the security is priced at its fair value (the amount that the owner might reasonably expect to receive upon the current sale of the security).

The values of any foreign securities held by a fund are converted into U.S. dollars using an exchange rate obtained from an independent third party as of the close of regular trading on the NYSE. The values of any mutual fund shares, including institutional money market fund shares, held by a fund are based on the NAVs of the shares. The values of any ETF shares or closed-end fund shares held by a fund are based on the market value of the shares.

A fund also will use fair-value pricing if the value of a security it holds has been materially affected by events occurring before the fund's pricing time but after the close of the principal exchange or market on which the security is traded. This most commonly occurs with foreign securities, which may trade on foreign exchanges that close many hours before the fund's pricing time. Intervening events might be company-specific (e.g., earnings report, merger announcement) or country-specific or regional/global (e.g., natural disaster, economic or political news, interest rate change, act of terrorism). Intervening events include price movements in U.S. markets that exceed a specified threshold or that are otherwise deemed to affect the value of foreign securities.

Fair-value pricing may be used for domestic securities—for example, if (1) trading in a security is halted and does not resume before the fund's pricing time or a security does not trade in the course of a day and (2) the fund holds enough of the security that its price could affect the NAV.

Fair-value prices are determined by Vanguard according to procedures adopted by the board of trustees. When fair-value pricing is employed, the prices of securities used by a fund to calculate the NAV may differ from quoted or published prices for the same securities.

The Fund has authorized certain financial intermediaries and their designees, and may, from time to time, authorize certain funds of funds for which Vanguard serves as the investment advisor (Vanguard Funds of Funds), to accept orders to buy or sell fund shares on its behalf. The Fund will be deemed to receive an order when accepted by the financial intermediary, its designee, or one of the Vanguard Funds of Funds, and the order will receive the NAV next computed by the Fund after such acceptance.

Vanguard fund share prices are published daily on our website at vanguard.com/prices.

Financial Highlights

Financial highlights information is intended to help you understand a fund’s performance for the past five years (or, if shorter, its period of operations). Certain information reflects financial results for a single fund share. Total return represents the rate that an investor would have earned or lost each period on an investment in a fund or share class (assuming reinvestment of all distributions). Effective XX, 2023, the predecessor fund reorganized into the Fund. The Fund did not commence operations until XX, 2023 and has no performance history as of the date of this Prospectus. As a result, the financial highlights included below represent the performance of the predecessor fund. This information has been obtained from the financial statements audited by XXXX, an independent registered public accounting firm, whose report, along with predecessor fund financial statements, is included in the predecessor fund’s most recent annual report to shareholders. You may obtain a free copy of the predecessor fund’s latest annual or semiannual report, which is available upon request.

Vanguard Extended Market Index Fund Investor Shares
[To be updated]

Investing With Vanguard

This section of the prospectus explains the basics of doing business with Vanguard. Vanguard fund shares can be held directly with Vanguard or indirectly through an intermediary, such as a bank, a broker, or an investment advisor. If you hold Vanguard fund shares directly with Vanguard, you should carefully read each topic within this section that pertains to your relationship with Vanguard. If you hold Vanguard fund shares indirectly through an intermediary (including shares held in a brokerage account through Vanguard Brokerage Services®), please see Investing With Vanguard Through Other Firms, and also refer to your account agreement with the intermediary for information about transacting in that account. If you hold Vanguard fund shares through an employer-sponsored retirement or savings plan, please see Employer-Sponsored Plans. Vanguard reserves the right to change the following policies without notice. Please call or check online for current information. See Contacting Vanguard.

For Vanguard fund shares held directly with Vanguard, each fund you hold in an account is a separate “fund account.” For example, if you hold three funds in a nonretirement account titled in your own name, two funds in a nonretirement account titled jointly with your spouse, and one fund in an individual retirement account, you have six fund accounts—and this is true even if you hold the same fund in multiple accounts. Note that each reference to “you” in this prospectus applies to any one or more registered account owners or persons authorized to transact on your account.

Purchasing Shares

Vanguard reserves the right, without notice, to increase or decrease the minimum amount required to open, convert shares to, or maintain a fund account or to add to an existing fund account.

Investment minimums may differ for certain categories of investors.

Account Minimums for Investor Shares

Investor Shares are generally available only to Vanguard funds that operate as funds of funds and to certain retirement plan clients that receive recordkeeping services from Vanguard. Other than these eligibility requirements, Investor Shares generally have no investment minimum.

How to Initiate a Purchase Request

Be sure to check Exchanging Shares, Frequent-Trading Limitations, and Other Rules You Should Know before placing your purchase request.

Online. You may open certain types of accounts, request a purchase of shares, and request an exchange through our website or our mobile application if your account is eligible and you are registered for online access.

By telephone. You may call Vanguard to begin the account registration process or request that the account-opening forms be sent to you. You may also call Vanguard to request a purchase of shares in your account or to request an exchange. See Contacting Vanguard.

By mail. You may send Vanguard your account registration form and check to open a new fund account. To add to an existing fund account, you may send your check with an Invest-by-Mail form (from a transaction confirmation or your account statement) or with a deposit slip (available online).

How to Pay for a Purchase

By electronic bank transfer. You may purchase shares of a Vanguard fund through an electronic transfer of money from a bank account. To establish the electronic bank transfer service on an account, you must designate the bank account online, complete a form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can purchase shares by electronic bank transfer on a regular schedule (Automatic Investment Plan), if eligible, or upon request. Your purchase request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. Wiring instructions vary for different types of purchases. Please call Vanguard for instructions and policies on purchasing shares by wire. See Contacting Vanguard.

By check. You may make initial or additional purchases to your fund account by sending a check with a deposit slip or by utilizing our mobile application if your account is eligible and you are registered for online access. Also see How to Initiate a Purchase Request. Make your check payable to Vanguard and include the appropriate fund number (Vanguard—98).

By exchange. You may purchase shares of a Vanguard fund using the proceeds from the simultaneous redemption of shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail with an exchange form. See Exchanging Shares.

Trade Date

that the NYSE is open for trading (a business day). In the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. The time selected for NAV calculation in this rare event shall also serve as the conclusion of the trading day. See Share Price.

For purchases by check into all funds other than money market funds and for purchases by exchange, wire, or electronic bank transfer into all funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the same day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the next business day.

For purchases by check into money market funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the next business day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the second business day following the day Vanguard receives the purchase request. Because money market instruments must be purchased with federal funds and it takes a money market mutual fund one business day to convert check proceeds into federal funds, the trade date for the purchase will be one business day later than for other funds.

If applicable, orders by Vanguard Funds of Funds will be treated as received by a Fund at the same time that corresponding orders are received in proper form by the Vanguard Funds of Funds.

If your purchase request is not accurate and complete, it may be rejected. See Other Rules You Should Know—Good Order.

For further information about purchase transactions, consult our website at vanguard.com or see Contacting Vanguard.

Other Purchase Rules You Should Know

Check purchases. All purchase checks must be written in U.S. dollars, be drawn on a U.S. bank, and be accompanied by good order instructions. Vanguard does not accept cash, traveler’s checks, starter checks, or money orders. In addition, Vanguard may refuse checks that are not made payable to Vanguard.

New accounts. We are required by law to obtain from you certain personal information that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your identity, Vanguard reserves the right, without notice, to close your account or take such other steps as we deem reasonable. Certain types of accounts may require additional documentation.

Refused or rejected purchase requests. Vanguard reserves the right to stop selling fund shares or to reject any purchase request at any time and without notice, including, but not limited to, purchases requested by exchange from another Vanguard fund. This also includes the right to reject any purchase request because the investor has a history of frequent trading or because the purchase may negatively affect a fund’s operation or performance.

Large purchases. Call Vanguard before attempting to invest a large dollar amount.

No cancellations. Vanguard will not accept your request to cancel any purchase request once processing has begun. Please be careful when placing a purchase request.

Converting Shares

When a conversion occurs, you receive shares of one class in place of shares of another class of the same fund. At the time of conversion, the dollar value of the “new” shares you receive equals the dollar value of the “old” shares that were converted. In other words, the conversion has no effect on the value of your investment in the fund at the time of the conversion. However, the number of shares you own after the conversion may be greater than or less than the number of shares you owned before the conversion, depending on the NAVs of the two share classes.

Vanguard will not accept your request to cancel any self-directed conversion request once processing has begun. Please be careful when placing a conversion request.

A conversion between share classes of the same fund is a nontaxable event.

Trade Date

the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. The time selected for NAV calculation in this rare event shall also serve as the conclusion of the trading day. See Share Price.

For a conversion request (other than a request to convert to ETF Shares) received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. For a conversion request received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day. See Other Rules You Should Know.

Conversions to Institutional Shares or Institutional Plus Shares

You are eligible for a self-directed conversion from another share class to Institutional Shares or Institutional Plus Shares of the Fund, provided that your account meets all eligibility requirements. You may request a conversion through our website (if you are registered for online access), or you may contact Vanguard by telephone or by mail to request this transaction. Accounts that qualify for Institutional Shares or Institutional Plus Shares will not be automatically converted.

Conversions to Institutional Select Shares

You are eligible for a self-directed conversion from another share class to Institutional Select Shares of the Fund, provided that your account meets all eligibility requirements. You may request a conversion through our website (if you are registered for online access), through a trading platform, by mail, or by telephone. Accounts that qualify for Institutional Select Shares will not be automatically converted.

Conversions to ETF Shares

Owners of conventional (i.e., not exchange-traded) shares issued by the Fund may convert those shares to ETF Shares of equivalent value of the same fund. Please note that investors who own conventional shares through a 401(k) plan or other employer-sponsored retirement or benefit plan generally may not convert those shares to ETF Shares and should check with their plan sponsor or recordkeeper. ETF Shares, whether acquired through a conversion or purchased on the secondary market, cannot be converted to conventional shares by a shareholder. Also, ETF Shares of one fund cannot be exchanged for ETF Shares of another fund.

ETF Shares must be held in a brokerage account. Thus, before converting conventional shares to ETF Shares, you must have an existing, or open a new, brokerage account. This account may be with Vanguard Brokerage Services or with any other brokerage firm.

Vanguard Brokerage Services does not impose a fee on conversions from conventional shares to Vanguard ETF Shares. However, other brokerage firms may charge a fee to process a conversion. Vanguard reserves the right, in the future, to impose a transaction fee on conversions or to limit, temporarily suspend, or terminate the conversion privilege. For additional information on converting conventional shares to ETF Shares, please contact Vanguard to obtain a prospectus for ETF Shares. See Contacting Vanguard.

Mandatory Conversions to Another Share Class

If an account no longer meets the balance requirements for a share class, Vanguard may automatically convert the shares in the account to another share class, as appropriate. A decline in the account balance because of market movement may result in such a conversion. Vanguard will notify the investor in writing before any mandatory conversion occurs.

Redeeming Shares

How to Initiate a Redemption Request

Be sure to check Exchanging Shares, Frequent-Trading Limitations, and Other Rules You Should Know before placing your redemption request.

Online. You may request a redemption of shares or request an exchange through our website or our mobile application if your account is eligible and you are registered for online access.

By telephone. You may call Vanguard to request a redemption of shares or an exchange. See Contacting Vanguard.

By mail. You may send a form (available online) to Vanguard to redeem from a fund account or to make an exchange.

How to Receive Redemption Proceeds

By electronic bank transfer. You may have the proceeds of a fund redemption sent directly to a designated bank account. To establish the electronic bank transfer service on an account, you must designate a bank account online, complete a form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can redeem shares by electronic bank transfer on a regular schedule (Automatic Withdrawal Plan), if

eligible, or upon request. Your redemption request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. To receive your proceeds by wire, you may instruct Vanguard to wire your redemption proceeds ($100 minimum) to a previously designated bank account. To establish the wire redemption service, you generally must designate a bank account online, complete a form, or fill out the appropriate section of your account registration form.

Please note that Vanguard charges a $10 wire fee for outgoing wire redemptions. The fee is assessed in addition to, rather than being withheld from, redemption proceeds and is paid directly to the fund in which you invest. For example, if you redeem $100 via a wire, you will receive the full $100, and the $10 fee will be assessed to your fund account through an additional redemption of fund shares. If you redeem your entire fund account, your redemption proceeds will be reduced by the amount of the fee. The wire fee does not apply to accounts held by Flagship and Flagship Select clients; accounts held through intermediaries, including Vanguard Brokerage Services; or accounts held by institutional clients.

By exchange. You may have the proceeds of a Vanguard fund redemption invested directly in shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail. See Exchanging Shares.

By check. If you have not chosen another redemption method, Vanguard will mail you a redemption check, generally payable to all registered account owners, normally within two business days of your trade date, and generally to the address of record.

Trade Date

The trade date for any redemption request received in good order will depend on the day and time Vanguard receives your request and the manner in which you are redeeming. Your redemption will be executed using the NAV as calculated on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day). In the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. The time selected for NAV calculation in this rare event shall also serve as the conclusion of the trading day. See Share Price.

For redemptions by check, exchange, or wire: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

• Note on timing of wire redemptions from money market funds: For telephone requests received by Vanguard on a business day before 10:45 a.m., Eastern time (2 p.m., Eastern time, for Vanguard Cash Reserves Federal Money Market Fund; 12:30 p.m., Eastern time, for Vanguard Federal Money Market Fund), the redemption proceeds generally will leave Vanguard by the close of business the same day. For telephone requests received by Vanguard on a business day after those cut-off times, or on a nonbusiness day, and for all requests other than by telephone, the redemption proceeds generally will leave Vanguard by the close of business on the next business day.

• Note on timing of wire redemptions from all other funds: For requests received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the redemption proceeds generally will leave Vanguard by the close of business on the next business day. For requests received by Vanguard on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the redemption proceeds generally will leave Vanguard by the close of business on the second business day after Vanguard receives the request.

For redemptions by electronic bank transfer: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

If your redemption request is not accurate and complete, it may be rejected. If we are unable to send your redemption proceeds by wire or electronic bank transfer because the receiving institution rejects the transfer, Vanguard will make additional efforts to complete your transaction. If Vanguard is still unable to complete the transaction, we may send the proceeds of the redemption to you by check, generally payable to all registered account owners, or use your proceeds to purchase new shares of the fund from which you sold shares for the purpose of the wire or electronic bank transfer transaction. See Other Rules You Should Know—Good Order.

If your redemption request is received in good order, we typically expect that redemption proceeds will be paid by the Fund within one business day of the trade date; however, in certain circumstances, investors may experience a longer settlement period at the time of the transaction. For further information, see “Potentially disruptive redemptions” and “Emergency circumstances.”

For further information about redemption transactions, consult our website at vanguard.com or see Contacting Vanguard.

Other Redemption Rules You Should Know

Documentation for certain accounts. Special documentation may be required to redeem from certain types of accounts, such as trust, corporate, nonprofit, or retirement accounts. Please call us before attempting to redeem from these types of accounts.

Potentially disruptive redemptions. Vanguard reserves the right to pay all or part of a redemption in kind—that is, in the form of securities—if we reasonably believe that a cash redemption would negatively affect the fund’s operation or performance or that the shareholder may be engaged in market-timing or frequent trading. Under these circumstances, Vanguard also reserves the right to delay payment of the redemption proceeds for up to seven calendar days. By calling us before you attempt to redeem a large dollar amount, you may avoid in-kind or delayed payment of your redemption. Please see Frequent-Trading Limitations for information about Vanguard’s policies to limit frequent trading.

Recently purchased shares. Although you can redeem shares at any time, proceeds may not be made available to you until the fund collects payment for your purchase. This may take up to seven calendar days for shares purchased by check or by electronic bank transfer. If you have written a check on a fund in an account with checkwriting privileges, that check may be rejected if your fund account does not have a sufficient available balance.

Share certificates. Share certificates are no longer issued for Vanguard funds. Shares currently held in certificates cannot be redeemed, exchanged, converted, or transferred (reregistered) until you return the certificates (unsigned) to Vanguard by registered mail.

Address change. If you change your address online or by telephone, there may be up to a 14-day restriction (starting on the business day after your address is changed) on your ability to request check redemptions online and by telephone. You can request a redemption in writing (using a form available online) at any time. Confirmations of address changes are sent to both the old and new addresses.

Payment to a different person or address. At your request, we can make your redemption check payable, or wire your redemption proceeds, to a different person or send it to a different address. However, this generally requires the written consent of all registered account owners and may require additional documentation, such as a signature guarantee or a notarized signature. You may obtain a signature guarantee from some commercial or savings banks, credit unions, trust companies, or member firms of a U.S. stock exchange.

No cancellations. Vanguard will not accept your request to cancel any redemption request once processing has begun. Please be careful when placing a redemption request.

Emergency circumstances. Vanguard funds can postpone payment of redemption proceeds for up to seven calendar days. In addition, Vanguard funds can suspend redemptions and/or postpone payments of redemption proceeds beyond seven calendar days at times when the NYSE is closed or during emergency circumstances, as determined by the SEC.

Exchanging Shares

An exchange occurs when you use the proceeds from the redemption of shares of one Vanguard fund to simultaneously purchase shares of a different Vanguard fund. You can make exchange requests online (if you are registered for online access), by telephone, or by mail. See Purchasing Shares and Redeeming Shares.

If the NYSE is open for regular trading (generally until 4 p.m., Eastern time, on a business day) at the time an exchange request is received in good order, the trade date generally will be the same day. See Other Rules You Should Know—Good Order for additional information on all transaction requests.

Vanguard will not accept your request to cancel any exchange request once processing has begun. Please be careful when placing an exchange request.

Call Vanguard before attempting to exchange a large dollar amount. By calling us before you attempt to exchange a large dollar amount, you may avoid delayed or rejected transactions.

Please note that Vanguard reserves the right, without notice, to revise or terminate the exchange privilege, limit the amount of any exchange, or reject an exchange, at any time, for any reason. See Frequent-Trading Limitations for additional restrictions on exchanges.

Frequent-Trading Limitations

Because excessive transactions can disrupt management of a fund and increase the fund’s costs for all shareholders, the board of trustees of each Vanguard fund places certain limits on frequent trading in the funds. Each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) limits an investor’s purchases or exchanges into a fund account for 30 calendar days after the investor has redeemed or exchanged out of that fund account. ETF Shares are not subject to these frequent-trading limits.

For Vanguard Retirement Investment Program pooled plans, the limitations apply to exchanges made online or by telephone.

These frequent-trading limitations do not apply to the following:

• Certain transactions below dollar value or other thresholds specified by Vanguard.

• In-kind transactions to a shareholder’s donor advised fund managed by Vanguard Charitable.

• Purchases of shares with reinvested dividend or capital gains distributions.

• Transactions through Vanguard’s Automatic Investment Plan, Automatic Exchange Service, Direct Deposit Service, Automatic Withdrawal Plan, Required Minimum Distribution Service, Vanguard Small Business Online®, and certain transactions through intermediaries relating to systematic trades and required minimum distributions.

• Discretionary transactions through Vanguard Personal Advisor Services®, Vanguard Institutional Advisory Services®, Vanguard Digital Advisor™, and discretionary (advisor-directed) transactions through certain intermediaries.

• Redemptions of shares to pay fund or account fees.

• Redemptions of shares to remove excess shareholder contributions to certain types of retirement accounts (including, but not limited to, IRAs and Vanguard Individual 401(k) Plans).

• Transfers and reregistrations of shares within the same fund.

• Purchases of shares by asset transfer or direct rollover.

• Conversions of shares from one share class to another in the same fund.

• Checkwriting redemptions.

• Section 529 college savings plans.

• Certain approved institutional portfolios and asset allocation programs, as well as trades made by funds or trusts managed by Vanguard or its affiliates that

invest in other Vanguard funds. (Please note that shareholders of Vanguard’s funds of funds are subject to the limitations.)

For participants in employer-sponsored defined contribution plans,* the frequent-trading limitations do not apply to:

• Purchases of shares with participant payroll or employer contributions or loan repayments.

• Purchases of shares with reinvested dividend or capital gains distributions.

• Distributions, loans, and in-service withdrawals from a plan.

• Redemptions of shares as part of a plan termination or at the direction of the plan.

• Transactions executed through the Vanguard Managed Account Program.

• Redemptions of shares to pay fund or account fees.

• Share or asset transfers or rollovers.

• Reregistrations of shares.

• Conversions of shares from one share class to another in the same fund.

• Exchange requests submitted by written request to Vanguard. (Exchange requests submitted by fax, if otherwise permitted, are subject to the limitations.)

* The following Vanguard fund accounts are also subject to the frequent-trading limitations: SEP-IRAs, SIMPLE IRAs, certain Individual 403(b)(7) Custodial Accounts, and Vanguard Individual 401(k) Plans.

Accounts Held by Institutions (Other Than Defined Contribution Plans)

Vanguard will systematically monitor for frequent trading in institutional clients’ accounts. If we detect suspicious trading activity, we will investigate and take appropriate action, which may include applying to a client’s accounts the 30-day policy previously described, prohibiting a client’s purchases of fund shares, and/or revoking the client’s exchange privilege.

Accounts Held by Intermediaries

When intermediaries establish accounts in Vanguard funds for the benefit of their clients, we cannot always monitor the trading activity of the individual clients. However, we review trading activity at the intermediary (omnibus) level, and if we detect suspicious activity, we will investigate and take appropriate action. If necessary, Vanguard may prohibit additional purchases of fund shares by an intermediary, including for the benefit of certain of the intermediary’s clients. Intermediaries also may monitor their clients’ trading activities with respect to Vanguard funds.

For those Vanguard funds that charge purchase and/or redemption fees, intermediaries will be asked to assess these fees on client accounts and remit these fees to the funds. The application of purchase and redemption fees and frequent-trading limitations may vary among intermediaries. There are no assurances that Vanguard will successfully identify all intermediaries or that intermediaries will properly assess purchase and redemption fees or administer frequent-trading limitations. If you invest with Vanguard through an intermediary, please read that firm’s materials carefully to learn of any other rules or fees that may apply.

Other Rules You Should Know

Prospectus and Shareholder Report Mailings

When two or more shareholders have the same last name and address, just one summary prospectus (or prospectus) and/or shareholder report may be sent in an attempt to eliminate the unnecessary expense of duplicate mailings. You may request individual prospectuses and reports by contacting our Client Services Department in writing, by telephone, or online. See Contacting Vanguard.

Vanguard.com

Registration. If you are a registered user of vanguard.com, you can review your account holdings; buy, sell, or exchange shares of most Vanguard funds; and perform most other transactions through our website. You must register for this service online.

Electronic delivery. Vanguard can deliver your account statements, transaction confirmations, prospectuses, certain tax forms, and shareholder reports electronically. If you are a registered user of vanguard.com, you can consent to the electronic delivery of these documents by logging on and changing your mailing preferences under “Account Maintenance.” You can revoke your electronic consent at any time through our website, and we will begin to send paper copies of these documents within 30 days of receiving your revocation.

Telephone Transactions

Automatic. When we set up your account, we will automatically enable you to do business with us by telephone, unless you instruct us otherwise in writing.

Proof of a caller’s authority. We reserve the right to refuse a telephone request if the caller is unable to provide the requested information or if we reasonably believe that the caller is not an individual authorized to act on the account. Before we allow a caller to act on an account, we may request the following information:

• Authorization to act on the account (as the account owner or by legal documentation or other means).

• Account registration and address.

• Fund name and account number, if applicable.

• Other information relating to the caller, the account owner, or the account.

Good Order

We reserve the right to reject any transaction instructions that are not in “good order.” Good order generally means that your instructions:

• Are provided by the person(s) authorized in accordance with Vanguard’s policies and procedures to access the account and request transactions.

• Include the fund name and account number.

• Include the amount of the transaction (stated in dollars, shares, or percentage).

Written instructions also must generally be provided on a Vanguard form and include:

• Signature(s) and date from the authorized person(s).

• Signature guarantees or notarized signatures, if required for the type of transaction. (Call Vanguard for specific requirements.)

• Any supporting documentation that may be required.

Good order requirements may vary among types of accounts and transactions. For more information, consult our website at vanguard.com or see Contacting Vanguard.

Vanguard reserves the right, without notice, to revise the requirements for good order.

Future Trade-Date Requests

Vanguard does not accept requests to hold a purchase, conversion, redemption, or exchange transaction for a future date. All such requests will receive trade dates as previously described in Purchasing Shares, Converting Shares, Redeeming Shares, and Exchanging Shares. Vanguard reserves the right to return future-dated purchase checks.

Accounts With More Than One Owner

If an account has more than one owner or authorized person, Vanguard generally will accept instructions from any one owner or authorized person.

Responsibility for Fraud

You should take precautions to protect yourself from fraud. Keep your account-related information private, and review any account confirmations, statements, or other information that we provide to you as soon as you receive them. Let us know immediately if you discover unauthorized activity or see something on your account that you do not understand or that looks unusual.

Vanguard will not be responsible for losses that result from transactions by a person who we reasonably believe is authorized to act on your account.

Uncashed Checks

Please cash your distribution or redemption checks promptly. Vanguard will not pay interest on uncashed checks. Vanguard may be required to transfer assets related to uncashed checks to a state under the state’s abandoned property law.

Dormant Accounts

If your account has no activity in it for a period of time, Vanguard may be required to transfer it to a state under the state’s abandoned property law, subject to potential federal or state withholding taxes.

Unusual Circumstances

If you experience difficulty contacting Vanguard online or by telephone, you can send us your transaction request on a Vanguard form by regular or express mail.

Investing With Vanguard Through Other Firms

You may purchase or sell shares of most Vanguard funds through a financial intermediary, such as a bank, a broker, or an investment advisor. Please consult your financial intermediary to determine which, if any, shares are available through that firm and to learn about other rules that may apply. Your financial intermediary can provide you with account information and any required tax forms. You may be required to pay a commission on purchases of mutual fund shares made through a financial intermediary.

Please see Frequent-Trading Limitations—Accounts Held by Intermediaries for information about the assessment of any purchase or redemption fees and the monitoring of frequent trading for accounts held by intermediaries.

Account Service Fee

Vanguard may charge a $25 account service fee on fund accounts that have a balance below $5,000,000 for any reason, including market fluctuation. The account service fee may be applied to both retirement and nonretirement fund accounts and may be assessed on fund accounts in all Vanguard funds, regardless of the account minimum. The fee, which will be collected by redeeming fund shares in the amount of $25, will be deducted from fund accounts subject to the fee once per calendar year.

Certain account types have alternative fee structures, including SIMPLE IRAs, Vanguard Retirement Investment Program pooled plans, and Vanguard Individual 401(k) Plans.

Low-Balance Accounts

The Fund reserves the right to liquidate a fund account whose balance falls below the account minimum for any reason, including market fluctuation. This liquidation policy applies to nonretirement fund accounts and accounts that are held through intermediaries. Any such liquidation will be preceded by written notice to the investor.

Right to Change Policies

In addition to the rights expressly stated elsewhere in this prospectus, Vanguard reserves the right, without notice, to (1) alter, add, or discontinue any conditions of purchase (including eligibility requirements), redemption, exchange, conversion, service, or privilege at any time and (2) alter, impose, discontinue, or waive any purchase fee, redemption fee, account service fee, or other fee charged to a shareholder or a group of shareholders. Changes may affect any or all investors. These actions will be taken when, at the sole discretion of Vanguard management, Vanguard believes they are in the best interest of a fund.

Account Restrictions

protect vulnerable investors; (6) freeze any account and/or suspend account services if Vanguard has received reasonable notice of a dispute regarding the assets in an account, including notice of a dispute between the registered or beneficial account owners; and (7) freeze any account and/or suspend account services upon initial notification to Vanguard of the death of an account owner.

Share Classes

Vanguard reserves the right, without notice, to change the eligibility requirements of its share classes, including the types of clients who are eligible to purchase each share class.

Shareholder Rights

The Fund's Agreement and Declaration of Trust, as amended, requires a shareholder bringing a derivative action on behalf of Vanguard Institutional Index Funds (the Trust) that is subject to a pre-suit demand to collectively hold at least 10% of the outstanding shares of the Trust or at least 10% of the outstanding shares of the series or class to which the demand relates and to undertake to reimburse the Trust for the expense of any counsel or advisors used when considering the merits of the demand in the event that the board of trustees determines not to bring such action. In each case, these requirements do not apply to claims arising under the federal securities laws to the extent that any such federal securities laws, rules, or regulations do not permit such application.

Fund and Account Updates

Confirmation Statements

We will send (or provide through our website, whichever you prefer) a confirmation of your trade date and the amount of your transaction when you buy, sell, exchange, or convert shares. However, we will not send confirmations reflecting only checkwriting redemptions or the reinvestment of dividend or capital gains distributions. For any month in which you had a checkwriting redemption, a Checkwriting Activity Statement will be sent to you itemizing the checkwriting redemptions for that month. Promptly review each confirmation statement that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on a confirmation statement, or Vanguard will consider the transaction properly processed.

Portfolio Summaries

We will send (or provide through our website, whichever you prefer) quarterly portfolio summaries to help you keep track of your accounts throughout the year. Each summary shows the market value of your account at the close of the statement period, as well as all distributions, purchases, redemptions, exchanges, transfers, and conversions for the current calendar quarter (or month). Promptly review each summary that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on the summary, or Vanguard will consider the transaction properly processed.

Tax Information Statements

For most accounts, Vanguard (or your intermediary) is required to provide annual tax forms to assist you in preparing your income tax returns. These forms are generally available for each calendar year early in the following year. Registered users of vanguard.com can also view certain forms through our website. Vanguard (or your intermediary) may also provide you with additional tax-related documentation. For more information, consult our website at vanguard.com or see Contacting Vanguard.

Annual and Semiannual Reports

We will send (or provide through our website, whichever you prefer) reports about Vanguard Extended Market Index Fund twice a year, in February and August. These reports include overviews of the financial markets and provide the following specific Fund information:

• Performance assessments and comparisons with industry benchmarks.

• Financial statements with listings of Fund holdings.

Portfolio Holdings

Please consult the Fund's Statement of Additional Information or our website for a description of the policies and procedures that govern disclosure of the Fund’s portfolio holdings.

Employer-Sponsored Plans

Your plan administrator or your employee benefits office can provide you with detailed information on how to participate in your plan and how to elect the Fund as an investment option.

• If you have any questions about the Fund or Vanguard, including those about the Fund’s investment objective, strategies, or risks, contact Vanguard Participant Services toll-free at 800-523-1188 or visit our website at vanguard.com.

• If you have questions about your account, contact your plan administrator or the organization that provides recordkeeping services for your plan.

• Be sure to carefully read each topic that pertains to your transactions with Vanguard.

Vanguard reserves the right to change its policies without notice to shareholders.

Transactions

Processing times for your transaction requests may differ among recordkeepers or among transaction and funding types. Your plan’s recordkeeper (which may also be Vanguard) will determine the necessary processing time frames for your transaction requests prior to submission to the Fund. Consult your recordkeeper or plan administrator for more information.

If Vanguard is serving as your plan recordkeeper and if your transaction involves one or more investments with an early cut-off time for processing or another trading restriction, your entire transaction will be subject to the restriction when the trade date for your transaction is determined.

Contacting Vanguard

Web
Vanguard.com	For the most complete source of Vanguard news For fund, account, and service information For most account transactions For literature requests 24 hours a day, 7 days a week

Phone
Investor Information 800-662-7447 (Text telephone for people with hearing impairment at 800-749-7273)	For fund and service information For literature requests
Client Services 800-662-2739 (Text telephone for people with hearing impairment at 800-749-7273)	For account information For most account transactions
Participant Services 800-523-1188 (Text telephone for people with hearing impairment at 800-749-7273)	For information and services for participants in employer-sponsored plans
Institutional Division 888-809-8102	For information and services for large institutional investors
Financial Advisor and Intermediary Sales Support 800-997-2798	For information and services for financial intermediaries including financial advisors, broker-dealers, trust institutions, and insurance companies
Financial Advisory and Intermediary Trading Support 800-669-0498	For account information and trading support for financial intermediaries including financial advisors, broker-dealers, trust institutions, and insurance companies

Additional Information

The Fund's Bylaws require, unless the Trust otherwise consents in writing, that the U.S. Federal District Courts be the sole and exclusive forum for the resolution of complaints under the Securities Act of 1933. This provision may limit a shareholder’s ability to bring a claim in a different forum and may result in increased shareholder costs in pursuing such a claim.

Vanguard Fund	Inception Date1	Newspaper Abbreviation	Vanguard Fund Number	CUSIP Number
Vanguard Extended Market Index Fund
Investor Shares	12/21/1987	Extnd	98	xx

1 Inception date of the predecessor fund.

CGS identifiers have been provided by CUSIP Global Services, managed on behalf of the American Bankers Association by Standard & Poor’s Financial Services, LLC, and are not for use or dissemination in a manner that would serve as a substitute for any CUSIP service. The CUSIP Database, ©2023 American Bankers Association. “CUSIP” is a registered trademark of the American Bankers Association.

CFA® is a registered trademark owned by CFA Institute.

advice.

S&P DOW JONES INDICES DOES NOT GUARANTEE THE ADEQUACY, ACCURACY, TIMELINESS AND/OR THE COMPLETENESS OF THE INDEX OR ANY DATA RELATED THERETO OR ANY COMMUNICATION, INCLUDING BUT NOT LIMITED TO, ORAL OR WRITTEN COMMUNICATION (INCLUDING ELECTRONIC COMMUNICATIONS) WITH RESPECT THERETO. S&P DOW JONES INDICES SHALL NOT BE SUBJECT TO ANY DAMAGES OR LIABILITY FOR ANY ERRORS, OMISSIONS, OR DELAYS THEREIN. S&P DOW JONES INDICES MAKES NO EXPRESS OR IMPLIED WARRANTIES, AND EXPRESSLY DISCLAIMS ALL WARRANTIES, OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR USE OR AS TO RESULTS TO BE OBTAINED BY VANGUARD, OWNERS OF VANGUARD EXTENDED MARKET INDEX FUND, OR ANY OTHER PERSON OR ENTITY FROM THE USE OF THE INDEX OR WITH RESPECT TO ANY DATA RELATED THERETO. WITHOUT LIMITING ANY OF THE FOREGOING, IN NO EVENT WHATSOEVER SHALL S&P DOW JONES INDICES BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES INCLUDING BUT NOT LIMITED TO, LOSS OF PROFITS, TRADING LOSSES, LOST TIME OR GOODWILL, EVEN IF THEY HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, WHETHER IN CONTRACT, TORT, STRICT LIABILITY, OR OTHERWISE. THERE ARE NO THIRD PARTY BENEFICIARIES OF ANY AGREEMENTS OR ARRANGEMENTS BETWEEN S&P DOW JONES INDICES AND VANGUARD, OTHER THAN THE LICENSORS OF S&P DOW JONES INDICES.

Glossary of Investment Terms

Capital Gains Distributions. Payments to mutual fund shareholders of gains realized on securities that a fund has sold at a profit, minus any realized losses.

Common Stock. A security representing ownership rights in a corporation.

Dividend Distributions. Payments to mutual fund shareholders of income from interest or dividends generated by a fund's investments.

Dow Jones U.S. Total Stock Market Float Adjusted Index. An index that represents the entire U.S. stock market and tracks more than 5,000 stocks, excluding shares of securities not available for public trading.

Expense Ratio. A fund's total annual operating expenses expressed as a percentage of the fund's average net assets. The expense ratio includes management and administrative expenses, but it does not include the transaction costs of buying and selling portfolio securities.

Inception Date. The date on which the assets of a fund (or one of its share classes) are first invested in accordance with the fund's investment objective. For funds with a subscription period, the inception date is the day after that period ends. Investment performance is generally measured from the inception date.

Indexing. A low-cost investment strategy in which a mutual fund attempts to track—rather than outperform—a specified market benchmark, or “index.”

Joint Committed Credit Facility. The Fund participates, along with other funds managed by Vanguard, in a committed credit facility provided by a syndicate of lenders pursuant to a credit agreement that may be renewed annually; each Vanguard fund is individually liable for its borrowings, if any, under the credit facility. The amount and terms of the committed credit facility are subject to approval by the Fund's board of trustees and renegotiation with the lender syndicate on an annual basis.

Median Market Capitalization. An indicator of the size of companies in which a fund invests; the midpoint of market capitalization (market price x shares outstanding) of a fund's stocks, weighted by the proportion of the fund's assets invested in each stock. Stocks representing half of the fund's assets have market capitalizations above the median, and the rest are below it.

Mutual Fund. An investment company that pools the money of many people and invests it in a variety of securities in an effort to achieve a specific objective over time.

New York Stock Exchange (NYSE). A stock exchange based in New York City that is open for regular trading on business days, Monday through Friday, from 9:30 a.m. to 4 p.m., Eastern time.

Return of Capital. A return of capital occurs when a fund's distributions exceed its earnings in a fiscal year. A return of capital is a return of all or part of your original investment or amounts paid in excess of your original investment in a fund. In general, a return of capital reduces your cost basis in a fund's shares and is not taxable to you until your cost basis has been reduced to zero.

Price/Earnings (P/E) Ratio. The current share price of a stock, divided by its per-share earnings (profits). A stock selling for $20, with earnings of $2 per share, has a price/earnings ratio of 10.

Securities. Stocks, bonds, money market instruments, and other investments.

Total Return. A percentage change, over a specified time period, in a mutual fund’s net asset value, assuming the reinvestment of all distributions of dividends and capital gains.

Volatility. The fluctuations in value of a mutual fund or other security. The greater a fund's volatility, the wider the fluctuations in its returns.

Yield. Income (interest or dividends) earned by an investment, expressed as a percentage of the investment’s price.

Connect with Vanguard®˃ vanguard.com

For More Information

If you would like more information about Vanguard Extended Market Index Fund, the following documents are available free upon request:

Annual/Semiannual Reports to Shareholders

Additional information about the Fund's investments will be available in the Fund's annual and semiannual reports to shareholders. In the annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund's performance during its last fiscal year.

Statement of Additional Information (SAI)

The SAI provides more detailed information about the Fund and is incorporated by reference into (and thus legally a part of) this prospectus.

To receive a free copy of the latest annual or semiannual report (once available) or the SAI, or to request additional information about the Fund or other Vanguard funds, please visit vanguard.com or contact us as follows:

If you are an individual investor:
Telephone: 800-662-7447; Text telephone for people with hearing impairment: 800-749-7273

If you are a participant in an employer-sponsored plan:
Telephone: 800-523-1188; Text telephone for people
with hearing impairment: 800-749-7273

If you are a current Vanguard shareholder and would like information about your account, account transactions, and/or account statements, please call:

Client Services Department
Telephone: 800-662-2739; Text telephone for people with hearing impairment: 800-749-7273

Information Provided by the SEC

Reports and other information about the Fund are available in the EDGAR database on the SEC’s website at sec.gov, or you can receive copies of this information, for a fee, by electronic request at the following email address: publicinfo@sec.gov.

Fund's Investment Company Act file number: 811-06093

Vanguard Extended Market Index Fund

Prospectus

XX, 2023

Admiral™ Shares

Vanguard Extended Market Index Fund Admiral Shares (VEXAX)

This prospectus contains financial data for the predecessor fund through the fiscal period ended xx, 2023.

The Securities and Exchange Commission (SEC) has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Contents

Fund Summary	1
Investing in Index Funds	6
More on the Fund	7
The Fund and Vanguard	15
Investment Advisor	15
Dividends, Capital Gains, and Taxes	17
Share Price	20
Financial Highlights	22

Investing With Vanguard	23
Purchasing Shares	23
Converting Shares	26
Redeeming Shares	28
Exchanging Shares	32
Frequent-Trading Limitations	33
Other Rules You Should Know	35
Fund and Account Updates	39
Employer-Sponsored Plans	41
Contacting Vanguard	42
Additional Information	43
Glossary of Investment Terms	45

Fund Summary

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of small- and mid-capitalization stocks.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy, hold, and sell Admiral Shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.

Shareholder Fees
(Fees paid directly from your investment)


Sales Charge (Load) Imposed on Purchases	None
Purchase Fee	None
Sales Charge (Load) Imposed on Reinvested Dividends	None
Redemption Fee	None
Account Service Fee Per Year (for certain fund account balances below $5,000,000)	$25

Annual Fund Operating Expenses
(Expenses that you pay each year as a percentage of the value of your investment)


Management Fees	[ ] %
12b-1 Distribution Fee	None
Other Expenses	[ ] %
Total Annual Fund Operating Expenses	[ ] %

Example

The following example is intended to help you compare the cost of investing in the Fund’s Admiral Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you were to redeem your investment at the end of the given period. 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
[ ]	[ ]	[ ]	[ ]

Portfolio Turnover

Principal Investment Strategies

Principal Risks

• Investment style risk, which is the chance that returns from small- and mid-capitalization stocks will trail returns from the overall stock market. Historically, small- and mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. The stock prices of small and mid-size companies tend to experience greater volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

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.

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. Performance shown below prior to XX, 2023, is that of Vanguard Extended Market Index Fund, a series of Vanguard Index Funds (the predecessor fund), which was reorganized into the Fund at the close of business on XX, 2023 (the reorganization). The predecessor fund was managed using the same investment policies, objectives, guidelines, and restrictions as those of the Fund. Prior to the reorganization, the Fund had not yet commenced operations. The bar chart shows how the performance of the Fund's Admiral Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Admiral Shares compare with those of the Fund’s target index and another comparative index, which have investment characteristics similar to those of the Fund. Keep in mind that the

Annual Total Returns — Vanguard Extended Market Index Fund Admiral Shares1

[To be updated]

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2023, was xx%.

During the periods shown in the bar chart, the highest and lowest returns for a calendar quarter were:

	Total Return	Quarter
Highest	[ ]
Lowest	[ ]

Average Annual Total Returns for Periods Ended December 31, 2022

	1 Year	5 Years	10 Years
Vanguard Extended Market Index Fund Admiral Shares
Return Before Taxes	[ ]	[ ]	[ ]
Return After Taxes on Distributions	[ ]	[ ]	[ ]
Return After Taxes on Distributions and Sale of Fund Shares	[ ]	[ ]	[ ]
Standard & Poor's Completion Index (reflects no deduction for fees, expenses, or taxes)	[ ]	[ ]	[ ]
Dow Jones U.S. Total Stock Market Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)	[ ]	[ ]	[ ]

Investment Advisor

The Vanguard Group, Inc. (Vanguard)

Portfolio Managers

Donald M. Butler, CFA, Principal of Vanguard. He has co-managed the Fund since its inception in XX 2023 and managed the predecessor fund since 1997 (co-managed since 2016).

Michelle Louie, CFA, Portfolio Manager at Vanguard. She has co-managed the Fund since its inception in XX 2023 and the predecessor fund since February 2023.

Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 982901, El Paso, TX 79998-2901), or by telephone (800-662-2739). The minimum investment amount required to open and maintain a Fund account for Admiral Shares is $3,000. The minimum investment amount required to add to an existing Fund account is generally $1. Financial intermediaries, institutional clients, and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Admiral Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

Investing in Index Funds

What Is Indexing?

Index funds typically have the following characteristics:

• Variety of investments. Depending on a fund’s benchmark index, the fund may invest in the securities of a variety of companies, industries, and/or governments or government agencies.

• Relative performance consistency. Because they seek to track market benchmarks, index funds usually do not perform dramatically better or worse than their benchmarks.

More on the Fund

Share Class Overview

This prospectus offers the Fund's Admiral Shares. Separate prospectuses offer the Fund's Investor Shares, which are generally available only to Vanguard funds that operate as funds of funds and to certain retirement plan clients that receive recordkeeping services from Vanguard, and Institutional Shares and Institutional Plus Shares, which are generally for investors who invest a minimum of $5 million and $100 million, respectively. Another prospectus offers Institutional Select Shares, which are generally for investors who invest a minimum of $3 billion. In addition, the Fund issues ETF Shares (an exchange-traded class of shares), which are also offered through a separate prospectus.

Plain Talk About Fund Expenses

All mutual funds have operating expenses. These expenses, which are

deducted from a fund’s gross income, are expressed as a percentage of the

net assets of the fund. Assuming that operating expenses remain as stated

in the Fees and Expenses section, Vanguard Extended Market Index Fund

Admiral Shares' expense ratio would be: 0.xx%, or $x.x0 per $1,000 of

average net assets.

Plain Talk About Costs of Investing

Costs are an important consideration in choosing a mutual fund. That is

because you, as a shareholder, pay a proportionate share of the costs of

operating a fund and any transaction costs incurred when the fund buys or

sells securities. These costs can erode a substantial portion of the gross

income or the capital appreciation a fund achieves. Even seemingly small

differences in expenses can, over time, have a dramatic effect on a

fund’s performance.

Market Exposure

The Fund is subject to stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund‘s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund‘s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

Security Selection

Other Investment Policies and Risks

To track its target index as closely as possible, the Fund attempts to remain fully invested in stocks. To help stay fully invested and to reduce transaction costs, the Fund may invest, to a limited extent, in derivatives, including equity futures. The Fund may also use derivatives such as total return swaps to obtain exposure to a stock, a basket of stocks, or an index. Generally speaking, a derivative is a financial contract whose value is based on the value of a financial asset (such as a stock, a bond, or a currency), a physical asset (such as gold, oil, or wheat), a market index, or a reference rate. Investments in derivatives may subject the Fund to risks different from, and possibly greater than, those of investments directly in the underlying securities or assets. The Fund will not use derivatives for speculation or for the purpose of leveraging (magnifying) investment returns.

Cash Management

Redemption Requests

Potential redemption activity impacts. At times, the Fund may experience adverse effects when certain large shareholders, or multiple shareholders comprising significant ownership of the Fund, redeem large amounts of shares of the Fund. Large redemptions may cause the Fund to sell portfolio securities at times when it would not otherwise do so. This may result in the Fund distributing capital gains or other taxable income to non-redeeming shareholders. Large redemptions may also increase the Fund's transaction costs. Redemption activity can occur for many reasons, including shareholder reactions to market movements or other events unrelated to Vanguard’s actions, or when Vanguard makes product changes that, for example, may result in a shareholder redeeming shares of the Fund to purchase shares of another similar fund or investment vehicle. When experiencing large redemptions, the Fund

reserves the right to pay all or part of the redemption in-kind and/or delay payment of the redemption proceeds for up to seven calendar days; see “Potentially disruptive redemptions” under Redeeming Shares in the Investing With Vanguard section.

Temporary Investment Measures

Frequent Trading or Market-Timing

Policies to address frequent trading. The Vanguard funds (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) do not knowingly accommodate frequent trading. The board of trustees of each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) has adopted policies and procedures reasonably designed to detect and discourage frequent trading and, in some cases, to compensate the fund for the costs associated with it. These policies and procedures do not apply to ETF Shares because frequent trading in ETF Shares generally does not disrupt portfolio management or otherwise harm fund shareholders. Although there is no assurance that Vanguard will be able to detect or prevent frequent trading or market-timing in all circumstances, the following policies have been adopted to address these issues:

• Certain Vanguard funds charge shareholders purchase and/or redemption fees on transactions.

See the Investing With Vanguard section of this prospectus for further details on Vanguard’s transaction policies.

Each Vanguard fund (other than retail and government money market funds), in determining its net asset value, will use fair-value pricing when appropriate, as described in the Share Price section. Fair-value pricing may reduce or eliminate the profitability of certain frequent-trading strategies.

Do not invest with Vanguard if you are a market-timer.

Turnover Rate

Although the Fund generally seek to invest for the long term, the Fund may sell securities regardless of how long they have been held. Generally, an index fund sells securities in response to redemption requests from shareholders of conventional (i.e., not exchange-traded) shares or to changes in the composition of its target index. Turnover rates for mid-cap and small-cap stock index funds tend to be higher than for large-cap stock index funds (although still relatively low, compared with actively managed stock funds) because the indexes they track are more likely to change as a result of companies merging, growing, or

failing. The Financial Highlights section of this prospectus shows historical turnover rates for the predecessor fund. A turnover rate of 100%, for example, would mean that the Fund had sold and replaced securities valued at 100% of its net assets within a one-year period. In general, the greater the turnover rate, the greater the impact transaction costs will have on a fund’s return. Also, funds with high turnover rates may be more likely to generate capital gains, including short-term capital gains, that must be distributed to shareholders and will be taxable to shareholders investing through a taxable account.

The Fund and Vanguard

Plain Talk About Vanguard’s Unique Corporate Structure

Vanguard is owned jointly by the funds it oversees and thus indirectly by the

shareholders in those funds. Most other mutual funds are operated by

management companies that are owned by third parties—either public or

private stockholders—and not by the funds they serve.

Investment Advisor

The Vanguard Group, Inc., P.O. Box 2600, Valley Forge, PA 19482, which began operations in 1975, serves as advisor to the Fund through its Equity Index Group. As of xx, 2023, Vanguard served as advisor for approximately $xx trillion in assets. Vanguard provides investment advisory services to the Fund pursuant to the Funds’ Service Agreement and subject to the supervision and oversight of the trustees and officers of the Fund.

For the fiscal period ended xx, 2023, the advisory expenses represented an effective annual rate of less than x.xx% of the predecessor fund’s average net assets. The Fund did not commence operations until xx, 2023.

advisor be hired, terminated, or replaced or that the terms of an existing advisory agreement be revised. The Fund have filed an application seeking a similar SEC exemption with respect to investment advisors that are wholly owned subsidiaries of Vanguard. If the exemption is granted, the Fund may rely on the new SEC relief.

The managers primarily responsible for the day-to-day management of the Fund are:

Michelle Louie, CFA, Portfolio Manager at Vanguard. She has been with Vanguard since 2010, has worked in investment management since 2011, has managed investment portfolios since 2016, and has co-managed the Fund since its inception in XX 2023 and the predecessor fund since February 2023. Education: B.S., The American University; M.B.A., Georgia Institute of Technology.

The Fund's Statement of Additional Information provides information about each portfolio manager’s compensation, other accounts under management, and ownership of shares of the Fund.

Dividends, Capital Gains, and Taxes

Fund Distributions

The Fund distributes to shareholders virtually all of its net income (interest and dividends, less expenses) as well as any net short-term or long-term capital gains realized from the sale of its holdings. From time to time, the Fund may also make distributions that are treated as a return of capital. Income dividends generally are distributed quarterly in March, June, September, and December; capital gains distributions, if any, generally occur annually in December. In addition, the Fund may occasionally make a supplemental distribution at some other time during the year.

You can receive distributions of income or capital gains in cash, or you can have them automatically reinvested in more shares of the Fund. However, if you are investing through an employer-sponsored retirement or savings plan, your distributions will be automatically reinvested in additional Fund shares.