BLACKROCK ETF TRUST

iShares Prime Money Market ETF

(the “Fund”)

Supplement dated March 3, 2025 to the Prospectus and Statement of Additional Information of the Fund, dated January 22, 2025, as supplemented to date

Effective immediately, the Fund’s Prospectus and Statement of Additional Information are amended as follows:

The section of the Prospectus entitled “More Information About the Fund—Principal Investments—Repurchase Agreements” is hereby deleted in its entirety and replaced with the following:

Repurchase Agreements. The Fund may enter into repurchase agreements. Repurchase agreements are similar in certain respects to collateralized loans, but are structured as a purchase of securities by the Fund, subject to the seller’s agreement to repurchase the securities at a mutually agreed upon date and price. Under a repurchase agreement, the seller is required to furnish collateral at least equal in value or market price to the amount of the seller’s repurchase obligation. Collateral for the Fund’s repurchase agreements may include cash, obligations issued by the U.S. Government or its agencies or instrumentalities, and obligations rated in the highest category by at least two nationally recognized statistical rating organizations (“NRSROs”), or, if unrated, determined to be of comparable quality by BFA pursuant to guidelines approved by the Board. For the Fund, however, collateral is not limited to the foregoing and may include, for example, obligations rated in any category by NRSROs. Additionally, collateral for a repurchase agreement may include other types of securities, including equity securities and other fixed income securities, that the Fund could not hold directly without the repurchase obligation.

The Fund may transfer uninvested cash balances into a single joint account at the Fund’s custodian bank, the daily aggregate balance of which will be invested in one or more repurchase agreements.

The section of the Statement of Additional Information entitled “Investment Strategies and Risks of the Fund—Investment Strategies and Policies—Repurchase Agreements” is hereby amended to delete the second paragraph thereof in its entirety and replace it with the following:

The securities subject to a repurchase agreement may bear maturities exceeding 397 days, provided the repurchase agreement itself matures in 397 days or less. The seller under a repurchase agreement will be required to maintain the value of the securities subject to the agreement at not less than the repurchase price (including accrued interest and any accrued premium). Collateral for the Fund’s repurchase agreements may include cash, obligations issued by the U.S. Government or its agencies or instrumentalities, and obligations rated in the highest category by at least two nationally recognized statistical rating organizations (“NRSROs”), or, if unrated, determined to be of comparable quality by BlackRock pursuant to guidelines approved by the Board. For the Fund, however, collateral is not limited to the foregoing and may include, for example, obligations rated in any category by NRSROs or include classes of CMOs issued by agencies and instrumentalities of the U.S. Government, such as IOs and POs, residual interests, PAC certificates and TAC certificates. Collateral for a repurchase agreement may also include securities, including equity securities and other fixed income securities, that the Fund could not hold directly without the repurchase obligation. The ratings by NRSROs represent their respective opinions as to the quality of the obligations they undertake to rate. Ratings, however, are general and are not absolute standards of quality. Consequently, obligations with the same rating, maturity, and interest rate may have different market prices. Appendix A to this SAI contains a description of the relevant rating symbols used by NRSROs for commercial paper that may be purchased by the Fund. See “Mortgage-Related and Other Asset-Backed Securities” for ratings information about IOs, POs, PACs and TACs.

Shareholders should retain this Supplement for future reference.

PRSAI-PMMF-0325SUP