Fidelity Flex® Funds

Fund/Ticker

Fidelity Flex® U.S. Bond Index Fund/FIBUX

Summary Prospectus

October 30, 2025

Before you invest, you may want to review the fund's prospectus, which contains more information about the fund and its risks. You can find the fund's prospectus, reports to shareholders, and other information about the fund (including the fund's SAI) online at fundresearch.fidelity.com/prospectus/sec. You can also get this information at no cost by calling 1-800-835-5095 or by sending an e-mail request to fidfunddocuments@fidelity.com. The fund's prospectus and SAI dated October 30, 2025 are incorporated herein by reference.

245 Summer Street, Boston, MA 02210

Fund Summary

Fund:

Fidelity Flex® U.S. Bond Index Fund

Investment Objective

Fidelity Flex® U.S. Bond Index Fund seeks to provide investment results that correspond to the aggregate price and interest performance of the debt securities in the Bloomberg U.S. Aggregate Bond Index.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions, which are not reflected in the tables and examples below.

Shareholder fees

(fees paid directly from your investment) None

Annual Operating Expenses

(expenses that you pay each year as a % of the value of your investment)

Management fee	0.00%
Distribution and/or Service (12b-1) fees	None
Other expenses	0.00%
Total annual operating expenses	0.00%A

AThe fund is available only to certain fee-based accounts and advisory programs offered by Fidelity. Advisory account clients, retirement plans, plan sponsors and/or plan participants typically pay an advisory fee that generally covers investment advisory and administrative services.

This example helps compare the cost of investing in the fund with the cost of investing in other funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. This example does not include any fees paid at the fee-based account or plan level. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

1 year	$	0
3 years	$	0
5 years	$	0
10 years	$	0

Portfolio Turnover

The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 68% of the average value of its portfolio.

Principal Investment Strategies

• Normally investing at least 80% of assets in bonds included in the Bloomberg U.S. Aggregate Bond Index.

The Bloomberg U.S. Aggregate Bond Index is a broad based, flagship benchmark that measures the investment grade, US dollar-denominated, fixed-rate taxable bond market. The index includes Treasuries, government-related and corporate securities, mortgage-backed securities (agency fixed-rate pass-throughs), asset-backed securities and collateralized mortgage-backed securities (agency and non-agency).

Effective December 11, 2025, derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives.

• Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg U.S. Aggregate Bond Index using a smaller number of securities.
• Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default), options, and futures contracts - and forward-settling securities, to adjust the fund's risk exposure.
• Investing in Fidelity's Central funds (specialized investment vehicles used by Fidelity® funds to invest in particular security types or investment disciplines) consistent with the asset classes discussed above.

Principal Investment Risks

• Interest Rate Changes.

Interest rate increases can cause the price of a debt security to decrease.

• Foreign Exposure.

Entities located in foreign countries can be affected by adverse political, regulatory, market, or economic developments in those countries.

• Prepayment.

The ability of an issuer of a debt security to repay principal prior to a security's maturity can cause greater price volatility if interest rates change.

• Issuer-Specific Changes.

The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole.

A decline in the credit quality of an issuer or a provider of credit support (such as guarantees) or a maturity-shortening structure (such as demand and put features) for a security can cause the price of a security to decrease.

• Correlation to Index.

The performance of the fund and its underlying index may vary somewhat due to factors such as fees and expenses of the fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from the index. Errors in the construction or calculation of the index may occur from time to time and may not be identified and corrected for some period of time, which may have an adverse impact on the fund and its shareholders.

• Passive Management Risk.

The fund is managed with a passive investment strategy, attempting to track the performance of an unmanaged index of securities, regardless of the current or projected performance of the fund's index or of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, the fund's performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Leverage Risk.

Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly.

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.You could lose money by investing in the fund.

Unlike individual debt securities, which typically pay principal at maturity, the value of an investment in the fund will fluctuate.

Performance

The following information is intended to help you understand the risks of investing in the fund.

The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time. The index description appears in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance.

The performance shown does not reflect the impact of any fees paid at the fee-based account or plan level.

Visit www.401k.com and log in or www.fidelity.com for more recent performance information.

Year-by-Year Returns

2018	2019	2020	2021	2022	2023	2024
0.11%	8.56%	7.72%	-1.89%	-12.96%	5.45%	1.30%

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	6.64%	December 31, 2023
Lowest Quarter Return	-5.79%	March 31, 2022
Year-to-Date Return	6.16%	September 30, 2025

Average Annual Returns

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes. Actual after-tax returns may differ depending on your individual circumstances. The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan). Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.

For the periods ended December 31, 2024	Past 1 year	Past 5 years	Life of fund
Fidelity Flex® U.S. Bond Index Fund
Return Before Taxes	1.30%	-0.35%	1.33% A
Return After Taxes on Distributions	-0.14%	-1.38%	0.22% A
Return After Taxes on Distributions and Sale of Fund Shares	0.80%	-0.67%	0.56% A
Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)	1.25%	-0.33%	1.37%

AFrom March 9, 2017.

Investment Adviser

Fidelity Management & Research Company LLC (FMR) (the Adviser) is the fund's manager. Other investment advisers serve as sub-advisers for the fund.

Portfolio Manager(s)

Brandon Bettencourt (Co-Portfolio Manager) has managed the fund since 2017.

Mark Lande (Co-Portfolio Manager) has managed the fund since 2024.

Van Eswara (Co-Portfolio Manager) has managed the fund since 2025.

Purchase and Sale of Shares

Shares are available only to certain fee-based accounts and advisory programs offered by Fidelity. Shares also may be available to certain broker-dealers that have entered into arrangements with Fidelity.

You may buy or sell shares in various ways:

Internet

Plan Accounts:	All Other Accounts:
www.401k.com	www.fidelity.com

Phone

Plan Accounts:

For Individual Accounts (investing through a retirement plan sponsor or other institution), refer to your plan materials or contact that institution directly.

For Retirement Plan Level Accounts:

Corporate Clients 1-800-962-1375

"Not for Profit" Clients 1-800-343-0860

All Other Accounts:

1-800-544-3455

Mail (Plan Accounts Only)

Redemptions: Fidelity Investments P.O. Box 770001 Cincinnati, OH 45277-0035 Overnight Express: Fidelity Investments 100 Crosby Parkway Covington, KY 41015

The price to buy one share is its net asset value per share (NAV). Shares will be bought at the NAV next calculated after an order is received in proper form.

The price to sell one share is its NAV. Shares will be sold at the NAV next calculated after an order is received in proper form.

The fund is open for business each day the New York Stock Exchange (NYSE) is open.

There is no purchase minimum for fund shares.

Tax Information

Distributions you receive from the fund are subject to federal income tax and generally will be taxed as ordinary income or capital gains, and may also be subject to state or local taxes, unless you are investing through a tax-advantaged retirement account (in which case you may be taxed later, upon withdrawal of your investment from such account).

Payments to Broker-Dealers and Other Financial Intermediaries

The Adviser, Fidelity Distributors Company LLC (FDC), and/or their affiliates may pay intermediaries, which may include banks, broker-dealers, retirement plan sponsors, administrators, or service-providers (who may be affiliated with the Adviser or FDC), for the sale of fund shares and related services. These payments may create a conflict of interest by influencing your intermediary and your investment professional to recommend the fund over another investment. Currently, the Board of Trustees of the fund has not authorized such payments for shares of the fund. Ask your investment professional or visit your intermediary's web site for more information.

"BLOOMBERG®" and the Bloomberg indices listed herein (the "Indices") are service marks of Bloomberg Finance L.P. and its affiliates, including Bloomberg Index Services Limited ("BISL"), the administrator of the Indices (collectively, "Bloomberg") and have been licensed for use for certain purposes by Fidelity. Bloomberg is not affiliated with Fidelity, and Bloomberg does not approve, endorse, review, or recommend the fund. Bloomberg does not guarantee the timeliness, accuracy, or completeness of any data or information relating to the fund.

Fidelity Distributors Company LLC (FDC) is a member of the Securities Investor Protection Corporation (SIPC). You may obtain information about SIPC, including the SIPC brochure, by visiting www.sipc.org or calling SIPC at 202-371-8300.

Fidelity, the Fidelity Investments Logo and all other Fidelity trademarks or service marks used herein are trademarks or service marks of FMR LLC. Any third-party marks that are used herein are trademarks or service marks of their respective owners. © 2025 FMR LLC. All rights reserved.

1.9880811.109 ZUB-SUM-1025