Firefly Aerospace Inc美股招股说明书(2026-03-20版)

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 Annual Report on Form 10-K, filed with the Securitiesand Exchange Commission on March19, 2026 (the “Annual Report”). Accordingly, we have attached the Annual 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”) ofup to 11,111,116 shares of Common Stock, par value $0.0001 per share (the “Common Stock”), of Firefly Aerospace Inc. (“Firefly Aerospace”) thatwere received by such Selling Securityholders as consideration in connection with Firefly Aerospace’s acquisition of SciTec Innovations, LLC, aDelaware limited 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 March18, 2026, the closing price of our Common Stock was$23.19 per share. Investing in our Common Stock involves risks. See “Risk Factors” beginning on page 12 of the Annual Report, and under similar headings inany further 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 March19, 2026. (Mark One)☒ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December31, 2025 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) 81-5194980(I.R.S. EmployerIdentification No.) 1320 Arrow Point Drive #109Cedar Park, TX(Address of principal executive offices) 512 893-5570Registrant’s telephone number, including area code Securities registered pursuant to Section12(b) of the Act: Title of each classTradingSymbol(s)Name of each exchangeon which registeredCommon Stock, $0.0001 par valueFLYThe Nasdaq Stock Market LLC (NasdaqGlobal Market) Securities registered pursuant to Section12(g) of the Act: None Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule405 of the Securities Act.Yes☐No☒ 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 of 1934during 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 405 ofRegulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit suchfiles).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 anemerging 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. Largeacceleratedfiler☐Non-accelerated filer☒ Accelerated filer☐Smallerreportingcompany☐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 anynew or revised financial accounting standards provided pursuant to Section13(a) of the Exchange Act.☐ Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internalcontrol over financial reporting under Section404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm thatprepared or issued its audit report.☐ If securities are registered pursuant to Section12(b) of the Act, indicate by check mark whether the financial statem