Firefly Aerospace Inc美股招股说明书(2026-05-04版)

Prospectus Supplement No.5(to Prospectus dated December19, 2025) 11,111,116 Shares This prospectus supplement updates and supplements the prospectus dated December19, 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 filedto update and supplement the information in the Prospectus with the information contained in our Quarterly Report on Form 10-Q, filed with theSecurities and Exchange Commission on May4, 2026 (the “Quarterly Report”). Accordingly, we have attached the Quarterly Report to this prospectussupplement. The Prospectus relates to the offer and sale from time to time by the selling securityholders named in the Prospectus (the “Selling Securityholders”) ofup to 11,111,116 shares of Common Stock, par value $0.0001 per share (the “Common Stock”) of Firefly Aerospace Inc. (“Firefly Aerospace”) that werereceived by such Selling Securityholders as consideration in connection with Firefly Aerospace’s acquisition of SciTec Innovations, LLC, a Delawarelimited liability company. This prospectus supplement should be read in conjunction with the Prospectus. This prospectus supplement updates and supplements the information inthe Prospectus. If there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on theinformation in this prospectus supplement. Our Common Stock is listed on the Nasdaq Global Market under the symbol “FLY”. On May1, 2026, the closing price of our Common Stock was$33.80 per share. Investing in our Common Stock involves risks. See “Risk Factors” beginning on page 9 of the Prospectus, and under similar headings in anyfurther amendments or supplements to the Prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities ordetermined 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 May4, 2026. (Mark One)☒QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 For the quarterly period ended March31, 2026 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 For 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) 81-5194980(I.R.S. EmployerIdentification Number) 78641(Zip Code) 512 893-5570(Registrant’s telephone number, including area code) N/A(Former name, former address and former fiscal year, if changed since last report) Securities registered pursuant to Section12(b) of the Act: Title of each classTradingSymbol(s)Name of each exchange on which registeredCommon Stock, $0.0001 par valueFLYThe Nasdaq Stock Market LLC (NasdaqGlobal Market) Indicate by check mark whether the registrant: (1)has filed all reports required to be filed by Section13 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 suchfiling requirements 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 Rule405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submitsuch 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-acceleratedfiler☒Emerginggrowthcompany☒ 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 Section13(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 April30, 2026, the registrant had 160,235,217 shares of common stock, $0.0001 par value, outstanding. Table of Contents FIREFLY AEROSPACE INC.QUARTERLY REPORT ON FORM 10-QTable of Contents PARTI.FINANCIAL INFORMATIONItem 1.Financial Statements (Unaudited)Condensed Consolidated Balance Sheets (Unaudited)Condensed Consolidated Statements of Net Loss and Comprehensive Loss (Unaudited)Condense