[424B3] USA Rare Earth, Inc. Prospectus Filed Pursuant to Rule 424(b)(3)

Rhea-AI Filing Summary

USA Rare Earth, Inc. filed a prospectus supplement to update its S-1 with a Form 8-K disclosing an auditor transition. Effective November 1, 2025, Horne LLP resigned after its partners and staff joined BDO USA, P.C., and the Audit Committee approved BDO as the new independent registered public accounting firm.

Horne’s reports on the Company’s 2024 and 2023 financial statements contained no adverse opinion, no disclaimer of opinion, and were not qualified or modified as to uncertainty, audit scope, or accounting principles. The Company reports no disagreements with Horne through October 31, 2025, and includes Horne’s concurrence letter as Exhibit 16.1.

USA Rare Earth’s securities trade on Nasdaq as USAR and USARW. On November 5, 2025, the Common Stock closed at $16.87 per share and the Warrants closed at $5.61 per Warrant.

Insights

Audit & Reporting Analyst

Auditor change to BDO; no disagreements reported.

USA Rare Earth appointed BDO USA, P.C. as independent auditor after Horne LLP’s partners and staff joined BDO, prompting Horne’s resignation effective November 1, 2025. The Audit Committee approved the appointment.

Horne’s audit reports for 2024 and 2023 carried no adverse or disclaimed opinions and were not qualified. The Company states there were no disagreements with Horne on accounting principles, disclosure, or audit scope through October 31, 2025.

The filing also includes Horne’s letter (Exhibit 16.1) acknowledging these statements. This appears administrative; actual impact on financial reporting depends on the routine transition to BDO’s audit processes.

Filed pursuant to Rule 424(b)(3)

Registration No. 333-290723

PROSPECTUS SUPPLEMENT No. 3

(to Prospectus dated October 27, 2025)

USA Rare Earth, Inc.

This prospectus supplement updates, amends and supplements the prospectus dated October 27, 2025 (the “Prospectus”), which forms a part of our Registration Statement on Form S-1 (Registration No. 333-290723). Capitalized terms used in this prospectus supplement and 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 the information contained in:

•our Current Report on Form 8-K filed with the SEC on November 6, 2025, which is set forth below.

This prospectus supplement is not complete without the Prospectus. This prospectus supplement should be read in conjunction with the Prospectus, which is to be delivered with this prospectus supplement, and is qualified by reference thereto, except to the extent that the information in this prospectus supplement updates or supersedes the information contained in the Prospectus. Please keep this prospectus supplement with your Prospectus for future reference.

USA Rare Earth, Inc.’s Common Stock and Warrants are listed on the Nasdaq Stock Market LLC under the symbols “USAR” and “USARW,” respectively. On November 5, 2025, the closing price of our Common Stock was $16.87 per share and the closing price of our Warrants was $5.61 per Warrant.

We are an “emerging growth company” and a “smaller reporting company” as such terms are defined under the federal securities laws and, 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 described under the heading “Risk Factors” of the Prospectus, and under similar headings in any amendments or supplements to the Prospectus.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if the Prospectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is November 6, 2025.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)
of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): November 1, 2025

USA Rare Earth, Inc.

(Exact Name of Registrant as Specified in its Charter)

Delaware

001-41711

98-1720278

(State or Other Jurisdiction of Incorporation)

(Commission File Number)

(I.R.S. Employer Identification No.)

100 W. Airport Road, Stillwater, OK 74075

(Address of Principal Executive Offices) (Zip Code)

(813) 867-6155

(Registrant’s telephone number, including area code)

Not applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Stock, par value $0.0001

USAR

The Nasdaq Stock Market LLC

Warrants, each whole warrant exercisable for one share of Common Stock, at an exercise price of $11.50 per share

USARW

The Nasdaq Stock Market LLC

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).

Emerging growth company  ☑

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Item 4.01    Changes in Registrant’s Certifying Accountant

Effective as of November 1, 2025, the partners and professional staff of Horne LLP (“Horne”), which was engaged as the independent registered public accounting firm of USA Rare Earth, Inc. (the “Company”), joined BDO USA, P.C. (“BDO”). As a result of this transaction, Horne resigned as the Company’s independent registered public accounting firm effective as of November 1, 2025. Effective as of November 1, 2025, following the resignation of Horne, the Company, through and with the approval of its Audit Committee, appointed BDO as its independent registered public accounting firm.

The report of Horne on the financial statements of the Company for the fiscal years ended December 31, 2024 and 2023, did not contain any adverse opinion or disclaimer of opinion and were not qualified or modified as to uncertainty, audit scope or accounting principles.

During the Company’s fiscal years ended December 31, 2024 and 2023, and through October 31, 2025, there were no disagreements between the Company and Horne on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which disagreements, if not resolved to the satisfaction of Horne, would have caused Horne to make reference to the subject matter of the disagreements in connection with its audit report on the Company’s financial statements. During the Company’s past fiscal years ended December 31, 2024 and 2023, and the interim period through October 31, 2025, Horne did not advise the Company of any of the matters specified in Item 304(a)(1)(v) of Regulation S-K.

The Company provided Horne with a copy of this report on Form 8-K in accordance with Item 304(a) of Regulation S-K prior to its filing with the Securities and Exchange Commission and requested that Horne furnish the Company with a letter addressed to the Securities and Exchange Commission stating whether it agrees with the above statements and, if it does not agree, the respects in which it does not agree. A copy of the letter from Horne is filed with this Report as Exhibit 16.1.

During the Company’s two most recently completed fiscal years and through the date of engagement of BDO, neither the Company nor anyone on behalf of the Company consulted with BDO regarding (a) the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the Company’s financial statements as to which the Company received a written report or oral advice that was an important factor in reaching a decision on any accounting, auditing or financial reporting issue; or (b) any matter that was the subject of a disagreement or a reportable event as defined in Items 304(a)(1)(iv)and (v), respectively, of Regulation S-K.

Item 9.01    Financial Statements and Exhibits

(d) Exhibits

Exhibit Number						Description
16.1						Letter from Horne LLP
104						Cover Page Interactive Data File (embedded within the inline XBRL document).

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

USA Rare Earth, Inc.

Date:

November 6, 2025

By:

/s/ DAVID KRONENFELD

David Kronenfeld

Chief Legal Officer

FAQ

What did USAR disclose in this prospectus supplement?

It updates the S-1 with an 8-K noting Horne LLP resigned and BDO USA, P.C. was appointed as independent auditor effective November 1, 2025.

Who is USA Rare Earth’s new auditor?

BDO USA, P.C., appointed with Audit Committee approval effective November 1, 2025.

Were there any disagreements with the prior auditor Horne LLP?

The Company reports no disagreements with Horne through October 31, 2025 on accounting principles, disclosure, or audit scope.

How were Horne’s prior audit opinions characterized?

Horne’s reports for 2024 and 2023 had no adverse opinions, no disclaimers, and were not qualified or modified.

Why did Horne LLP resign as auditor for USAR?

Horne’s partners and professional staff joined BDO, leading to Horne’s resignation and the appointment of BDO.

What are USAR’s Nasdaq tickers and recent closing prices?

Common Stock: USAR closed at $16.87 on Nov 5, 2025; Warrants: USARW closed at $5.61.