USA Rare Earth Inc 美股招股说明书（2026年3月12日版）

This prospectus supplement updates, amends and supplements the prospectus dated October 27, 2025 (the “Prospectus”), which formsa part of our Registration Statement on Form S-1 (Registration No. 333-290723). Capitalized terms used in this prospectus supplementand not otherwise defined herein have the meanings specified in the Prospectus. This prospectus supplement is being filed to update, amend and supplement the information included in the Prospectus with theinformation contained in: ●our Current Report on Form 8-K filed with the SEC on March 12, 2026, excluding Item 7.01 and Exhibit 99.1, which is setforth below. This prospectus supplement is not complete without the Prospectus. This prospectus supplement should be read in conjunction withthe Prospectus, which is to be delivered with this prospectus supplement, and is qualified by reference thereto, except to the extent that USA Rare Earth, Inc.’s Common Stock is listed on the Nasdaq Stock Market LLC under the symbol “USAR”. On March 11, 2026, theclosing price of our Common Stock was $21.09 per share. We are an “emerging growth company” and a “smaller reporting company” as such terms are defined under the federal securities lawsand, as such, are subject to certain reduced public company reporting requirements. Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties describedunder the heading “Risk Factors” of the Prospectus, and under similar headings in any amendments or supplements to the Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if theProspectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense. The date of this prospectus supplement is March 12, 2026. CURRENT REPORT 98-1720278 (I.R.S. EmployerIdentification No.) Securities registered pursuant to Section 12(b) of the Act: Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933(§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period forcomplying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐ Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; CompensationArrangements of Certain Officers. Resignation of Director; Appointment of Director On March 9, 2026, Tready Smith resigned from the Board of Directors (the “Board”) of USA Rare Earth, Inc. (the“Company”), and the Board subsequently appointed Thomas Caulfield as a director of the Company, filling the vacancy resulting fromMs. Smith’s resignation, such that the Board continues to have a total of eight directors serving on the Board. Additionally, the Board Dr. Caulfield is the Executive Chairman of GlobalFoundries (Nasdaq: GFS) and previously served, from 2018 to 2025 as thePresident and Chief Executive Officer of GlobalFoundries. Dr. Caulfield also serves as a board member of Sandisk Corp. The Boardhas determined that Dr. Caulfield qualifies as an independent director for service on the Board and the committees to which he wasassigned under Nasdaq Listing Rules. Dr. Caulfield will participate in the Company’s standard director compensation program as Item 7.01 Regulation FD Disclosure. On March 12, 2026, the Company issued a press release announcing both the appointment of Dr. Caufield and resignation ofMs. Smith. A copy of the press release is furnished herewith as Exhibit 99.1 and is incorporated by reference herein. The information provided under this Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1, is “furnished” andshall not be deemed “filed” with the SEC or incorporated by reference in any filing under the Securities Exchange Act of 1934, as Item 8.01. Other Events. On March 9, 2026, the Board determined that the date for its2026 AnnualMeeting of Shareholders will be June 3, 2026. Thetime and other meeting details for the 2026 Annual Meeting of Shareholders will be set forth in the Company’s proxy statement for the Because this will be the Company’s first annual meeting of shareholders, shareholders who wish to present a proposal to beconsidered for inclusion in the Company’s proxy materials pursuant to Rule 14a-8 under the Exchange Act for the 2026 AnnualMeeting of Shareholders must submit such proposal to the Company’s Secretary by April 1, 2026, which the Company has determined Item 9.01. Financial Statements and Exhibits. (d) Exhibits: The following exhibits are attached with this current report on Form 8-K: SIGNATURES