flagstar金融公司美股招股说明书(2025-10-08版)

Flagstar Financial, Inc. This prospectus supplement amends and supplements the prospectus dated May8, 2025, as amended or supplemented fromtime to time (the “Prospectus”), which forms a part of our Registration Statement on Form S-1 (No. 333-280398). This prospectussupplement is being filed to update and supplement the information in the Prospectus with the information contained in our CurrentReport on Form 8-K filed with the Securities and Exchange Commission on October7, 2025 (the “Form 8-K”). Accordingly, we haveattached the Form 8-K to this prospectus supplement. The Prospectus and this prospectus supplement relate to the offer and sale from time to time by the selling securityholderslisted in the section of the Prospectus entitled “Selling Securityholders” of up to (i) 263,828,622 shares of our common stock, parvalue $0.01 per share (“Common Stock”), and (ii) 314,954 net-settled warrants (“Warrants”). The shares of Common Stock andWarrants are referred to as the “Securities” herein. This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and maynot be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. Thisprospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information inthe Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement. Investing in the Securities involves a high degree of risk. See “Risk Factors” beginning on page 11 of the Prospectus. Our Common Stock is listed on the New York Stock Exchange (the “NYSE”) under the symbol “FLG.” On October7, 2025,the closing price of our Common Stock on the NYSE was $12.07 per share. The Warrants are not listed for trading on the NYSE orany other national securities exchange. Neither the Securities and Exchange Commission nor any other state securities commission has approved ordisapproved of the Securities or passed on the adequacy or accuracy of the Prospectus or this prospectus supplement. Anyrepresentation to the contrary is a criminal offense. The date of this prospectus supplement is October7, 2025 UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): October 3, 2025 FLAGSTAR FINANCIAL, INC.(Exact Name of Registrant as Specified in Charter) 06-1377322 (IRS Employer Identification No.) Securities registered pursuant to Section 12(b) of the Exchange Act: Common stock, $0.01 par value per shareBifurcated Option Note Unit Securities SMDepositary Shares each representing a 1/40th interestin a share of Fixed-to-Floating Rate Series ANoncumulative Perpetual Preferred Stock Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrantunder 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)) Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act (17 CFR230.405) or Rule 12b-2 of the Exchange Act (17 CFR 240.12b-2). Emerging growth company 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 ExchangeAct.☐ On October 3, 2025, the Office of the Comptroller of the Currency approved the application of Flagstar Financial, Inc. (the“Company”) to reorganize as a federal interim savings bank and immediately thereafter merge with and into Flagstar Bank, NationalAssociation (“Flagstar Bank”), with Flagstar Bank as the surviving entity. As a result of the transaction, Flagstar Bank will becomepublicly traded on the New York Stock Exchange. The transaction remains subject to approval of the Company’s shareholders, whichwill be considered at a meeting scheduled for October 15, 2025. Subject to obtaining shareholder approval, the Company expects thetransaction to close in mid-to late- October 2025. Item9.01Financial Statements and Exhibits (d) Attached as Exhibit 99.1 is the press release issued by the Company on October 6, 2025 announcing the receipt of OCC approvalof internal reorganization and merger. ExhibitDescription of ExhibitNo.99.1Press release issued by the Company on October 6, 2025104Cover Page Interactive Data File (embedded within the Inline XBRL document). SIGNATURE Pursuant