Firefly Aerospace美股招股说明书(2026-08-11版)

This prospectus supplement updates and supplements the prospectus dated December 19, 2025, as supplemented or amended from time to time (the“Prospectus”), which forms a part of our Registration Statement on Form S-1 (Registration No. 333-291599). This prospectus supplement is being filed toupdate and supplement the information in the Prospectus with the information contained in our Quarterly Report on Form 10-Q, filed with the Securities andExchange Commission on August 11, 2026 (the “Current Report”). Accordingly, we have attached the Quarterly Report to this prospectus supplement. The Prospectus relates to the offer and sale from time to time by the selling securityholders named in the Prospectus (the “Selling Securityholders”) of up to11,111,116 shares of Common Stock, par value $0.0001 per share (the “Common Stock”) of Firefly Aerospace Inc. (“Firefly Aerospace”) that were receivedby such Selling Securityholders as consideration in connection with Firefly Aerospace’s acquisition of SciTec Innovations, LLC, a Delaware limited liabilitycompany. This prospectus supplement should be read in conjunction with the Prospectus. This prospectus supplement updates and supplements the information in theProspectus. If there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in thisprospectus supplement. Our Common Stock is listed on the Nasdaq Global Market under the symbol “FLY”. On August 10, 2026, the closing price of our Common Stock was $25.76 Investing in our Common Stock involves risks. See “Risk Factors” beginning on page 9 of the Prospectus, and under similar headingsin any further amendments or supplements to the Prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securitiesor determined if the Prospectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminaloffense. UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 ☒QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934For the quarterly period ended June 30, 2026 or ☐TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934For the transition period from ___________ to ___________ Commission File Number: 001-42789 Firefly Aerospace Inc.(Exact name of registrant as specified in its charter) Delaware(State or other jurisdiction ofincorporation or organization)2203 Scottsdale DriveLeander, TX(Address of principal executive offices) 512 893-5570 (Registrant’s telephone number, including area code) (Former name, former address and former fiscal year, if changed since last report) Securities registered pursuant to Section 12(b) of the Act: TradingSymbol(s) The Nasdaq Stock Market LLC (Nasdaq Global Market) Common Stock, $0.0001 par value Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filingrequirements for the past 90 days. Yes☒No☐ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).Yes☒No☐ Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company,or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growthcompany” in Rule 12b-2 of the Exchange Act. Large accelerated filer☐Non-accelerated filer☒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 withany new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐ Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).Yes☐No☒As of August 6, 2026, the registrant had 167,404,645 shares of common stock, $0.0001 par value, outstanding. FIREFLY AEROSPACE INC.QUARTERLY REPORT ON FORM 10-QTable of Contents PART I.FINANCIAL INFORMATION Item 1.Financial Statements (Unaudited)6Condensed Consolidated Balance Sheets (Unaudited)6Condensed Consolidated Statements of Net Loss and Comprehensive Loss (Unaudited)7Condensed Consolidated Statements of Cash Flows (Unaudited)8Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Unaudited)10Notes to Condensed Consolidated Financial Sta