BRIDGE BUILDER TRUST

Bridge Builder Small/Mid Cap Growth Fund (the “Fund”)

Supplement dated September 21, 2026

to the Statement of Additional Information (“SAI”) dated October 27, 2025, as supplemented

This supplement provides new and additional information beyond that contained in the

SAI and should be read in conjunction with the SAI.

At a meeting held on August 19-20, 2026, the Board of Trustees of Bridge Builder Trust (the “Trust”), upon the recommendation of Olive Street Investment Advisers, LLC, approved certain changes to the Fund, including (i) a change to the Fund’s name to “Bridge Builder Mid Cap Fund,” (ii) changes to the Fund’s principal investment strategy pursuant to which the Fund will invest primarily in mid-capitalization companies and no longer invest primarily in both small- and mid-capitalization companies or follow a growth-oriented investment style, and (iii) a new 80% investment policy to invest in securities of mid-capitalization companies (collectively, the “Repositioning”). The Trust provided shareholders with notice of the Repositioning, including advance notice of the Fund’s new 80% investment policy pursuant to Rule 35d-1 under the Investment Company Act of 1940, in a supplement dated August 24, 2026 (the “August Supplement”). The Repositioning is expected to be completed by October 28, 2026.

In connection with the Repositioning, the Board also approved the appointment of certain new sub-advisers and the termination of certain existing sub-advisory agreements, as previously disclosed in the August Supplement. The Fund is now beginning to implement changes in connection with the Repositioning on a phased basis.

The changes described in this supplement are expected to be implemented in accordance with the approximate dates set forth below:

Effective on or about the same date, LSV Asset Management (“LSV”) and Vaughan Nelson Investment Management, L.P. (“Vaughan Nelson”) will each begin serving as a subadviser to an allocated portion of the Fund. Accordingly, the revisions described below relating to Eagle, Federated MDT, LSV and Vaughan Nelson will become effective on or about September 25, 2026.

Artisan Partners Limited Partnership, Driehaus Capital Management LLC, Los Angeles Capital Management LLC, Russell Investment Management, LLC and Stephens Investment Management Group, LLC will continue to serve as subadvisers to the Fund.

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Accordingly, the SAI is hereby supplemented and revised as follows:

Boston Partners Global Investors, Inc. (“Boston Partners”), One Beacon Street, 30^th Floor, Boston, MA 02108, is the Sub-adviser for an allocated portion of the Small/Mid Cap Growth Fund pursuant to a Sub-advisory Agreement with the Adviser. Boston Partners is an autonomous subsidiary of ORIX Corporation, a financial services holding company based in Japan. For its services as a Sub-adviser, Boston Partners is entitled to receive a fee from the Small/Mid Cap Growth Fund.

Other Accounts Managed by Portfolio Managers and Ownership of Fund Shares. The table below identifies, for each portfolio manager of the Fund, the number of accounts managed (excluding the Fund) and the total assets in such accounts, within each of the following categories: registered investment companies, other pooled investment vehicles, and other accounts. To the extent that any of these accounts are subject to a performance-based advisory fee, this information is reflected in the table below. Information is shown as of June 30, 2026. Asset amounts are approximate and have been rounded.

As of June 30, 2026, the above-listed portfolio managers did not beneficially own any shares of the Fund.

Potential Conflicts of Interest. Investment decisions for the Fund’s portfolio are made in conjunction with decisions for other accounts and/or funds for the same strategy. Boston Partners recognizes that potential conflicts may arise with respect to the side-by-side management of registered investment companies and “investment accounts,” which include privately offered funds, separately managed accounts of high net worth individuals and institutional investors, and the other funds. These risks include, but may not be limited to:

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differing fee structures (including performance based fees), differing investments selected for various vehicles, and inequitable allocation and aggregation trading practices. Private investment partnerships, registered funds and separately managed accounts are generally invested pari passu thus mitigating many of the perceived risks associated with simultaneous management if possible. Additionally, the Compliance Department has developed comprehensive monitoring policies and procedures designed to mitigate any actual or perceived conflicts.

Compensation. All investment professionals receive a compensation package comprised of an industry competitive base salary, a discretionary bonus and long-term incentives. Through the bonus program offered at Boston Partners, key investment professionals are rewarded primarily for strong investment performance. Boston Partners believes this aligns its team firmly with its clients’ objectives and provides the financial and work environment incentives which keep its teams in place.

Typically, bonuses are based upon a combination of one or more of the following four criteria:

The long-term incentive program offered by Boston Partners effectively confers a significant 20-30% ownership interest in the value of the business to key employees. Annual awards are made by the Compensation Committee and are meant to equate to an additional 10-20% of the participants cash bonus awards.

The compensation program focuses on long term performance with an emphasis on 3- and 5-year results. The timing of receiving deferred compensation reinforces this emphasis. Roughly 50% of compensation is based on qualitative measures and roughly 50% is based on quantitative measures. These compensation percentages can vary based on an individual’s role in the firm.

Boston Partners retains professional compensation consultants with asset management expertise to periodically review its practices to ensure that they remain highly competitive.

LSV Asset Management (“LSV”), 155 North Wacker Drive, Suite 4600, Chicago, IL 60606, is the Sub-adviser for an allocated portion of the Small/Mid Cap Growth Fund pursuant to a Sub-advisory Agreement with the Adviser. LSV is a Delaware general partnership between LSV’s management team and current and retired employee partners, owners of a majority position, and SEI Funds, Inc., a wholly-owned subsidiary of SEI Investments Company and the owner of a minority position. Both SEI Funds, Inc. and SEI Investments Company are located at 1 Freedom Valley Drive, Oaks, Pennsylvania 19456. For its services as a Sub-adviser, LSV is entitled to receive a fee from the Small/Mid Cap Growth Fund.

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Other Accounts Managed by Portfolio Managers and Ownership of Fund Shares. The table below identifies, for each portfolio manager of the Fund, the number of accounts managed (excluding the Fund) and the total assets in such accounts, within each of the following categories: registered investment companies, other pooled investment vehicles, and other accounts. To the extent that any of these accounts are subject to a performance-based advisory fee, this information is reflected in the table below. Information is shown as of June 30, 2026. Asset amounts are approximate and have been rounded.

As of June 30, 2026, the above-listed portfolio managers did not beneficially own any shares of the Fund.

Material Conflicts. The same team of portfolio managers is responsible for the day-to-day management of all of LSV’s accounts. LSV uses a proprietary quantitative investment model to manage all of LSV’s accounts. LSV relies extensively on its quantitative investment model regarding the advisability of investing in a particular company. Any investment decisions are generally made based on whether a buy or sell signal is received from the proprietary

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quantitative investment model. Accounts or funds with performance-based fees and accounts or funds in which employees may be invested could create an incentive to favor those accounts or funds over other accounts or funds in the allocation of investment opportunities. In addition, it is possible that a short position may be taken on a security that is held long in another portfolio. LSV seeks to make allocations of investment opportunities in a manner that it considers fair, reasonable and equitable without favoring or disfavoring, consistently or consciously, any particular client. LSV has procedures designed to ensure that all clients are treated fairly and to prevent these potential conflicts from influencing the allocation of investment opportunities among clients. On a quarterly basis, the Forensic Testing Committee reviews, among other things, allocations of investment opportunities among clients and the allocation of partially-filled block trades, including allocations to accounts or funds with performance-based fees or which employees may be invested, to confirm consistency with LSV’s policies and procedures.

Compensation. Dr. Lakonishok and Messrs. Vermeulen, Mansharamani, Sleight, G. Lakonishok, and Skarishevsky receive a fixed base salary and bonus which is a function of overall firm profitability and individual performance. Individual performance is subjective and may be based on a number of factors, such as the individual’s leadership and contribution to the strategic planning and development of the investment group. In addition, each of the portfolio managers is a partner of LSV and thereby receives a portion of the overall profit of the firm as part of his ownership interests.

Vaughan Nelson Investment Management, L.P. (“Vaughan Nelson”), located at 600 Travis Street, Houston, Texas 77002, is the Sub-adviser for an allocated portion of the Small/Mid Cap Growth Fund pursuant to a Sub-advisory Agreement with the Adviser. Vaughan Nelson is a wholly-owned subsidiary of Natixis Investment Managers LLC. For its services as a Sub-adviser, Vaughan Nelson is entitled to receive a fee from the Small/Mid Cap Growth Fund.

Other Accounts Managed by Portfolio Managers and Ownership of Fund Shares. The table below identifies, for each portfolio manager of the Fund, the number of accounts managed (excluding the Fund) and the total assets in such accounts, within each of the following categories: registered investment companies, other pooled investment vehicles, and other accounts. To the extent that any of these accounts are subject to a performance-based advisory fee, this information is reflected in the table below. Information is shown as of June 30, 2026. Asset amounts are approximate and have been rounded.

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As of June 30, 2026, the above-listed portfolio managers did not beneficially own any shares of the Fund.

Material Conflicts. At Vaughan Nelson, conflicts of interest may arise in the allocation of investment opportunities and the allocation of aggregated orders among the Fund and other accounts managed by the portfolio managers. A portfolio manager potentially could give favorable treatment to some accounts for a variety of reasons, including favoring larger accounts, accounts that pay higher fees, accounts that pay performance-based fees, accounts of affiliated companies and accounts in which the portfolio manager has an interest. Such favorable treatment could lead to more favorable investment opportunities or allocations for some accounts. Vaughan Nelson has adopted policies and procedures to mitigate the effects of these conflicts. A conflict of interest also may arise to the extent a portfolio manager short sells a stock or otherwise takes a short position in one client account but holds that stock long in other accounts, including the Fund, or sells a stock for some accounts while buying the stock for others. Another conflict which exists is the use of client commissions where a commission is paid to a broker or dealer that provides brokerage and/or research services in excess of the commission that would be charged by another broker or dealer for merely executing the same transaction (“soft dollar arrangements”).

Compensation. The compensation program at Vaughan Nelson is designed to align the interests of portfolio management professionals with the interests of clients and Vaughan Nelson by retaining top-performing employees and creating incentives to enhance Vaughan Nelson’s long-term success.

Compensation of portfolio management professionals includes a fixed base salary, a variable bonus and deferral plan and a contribution to the firm’s retirement plan.

All portfolio management professionals (at the discretion of the Compensation Committee of the Vaughan Nelson Board) participate in the variable bonus and deferral plan component which, as a whole, is based upon a percentage of Vaughan Nelson’s net profit. Each portfolio management professional’s participation in the variable bonus and deferral plan is based upon many factors, including but not limited to:

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The degree to which any one factor influences participation in the bonus pool will vary between individuals and over time. A portion of the variable bonus is subject to deferral and each participant has the option to invest the deferral into Vaughan Nelson managed product(s) while it vests. Each year’s deferral is paid out over a period of three years. Payments are conditioned upon compliance with non-compete and non-solicitation arrangements.

The contribution to the firm’s retirement plan is based on a percentage (at the discretion of the Vaughan Nelson Board) of total cash compensation (subject to the IRS limits) and such percentage is the same for all firm personnel. Compensation at Vaughan Nelson is determined by the Compensation Committee at the recommendation of the Chief Executive Officer.

There is no distinction for purposes of compensation between the Fund and any other accounts managed.

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE

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