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

Common Stock 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 Current Report on Form 8-K, filed with the Securitiesand Exchange Commission on March3, 2026 (the “Current Report”). Accordingly, we have attached the Current 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”) 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 March2, 2026, the closing price of our Common Stock was$20.92 per share. Investing in our Common Stock involves risks. See “Risk Factors” beginning on page 9 of the Prospectus, and undersimilar headings in 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 securities ordetermined if the Prospectus or this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense. UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 FORM 8-K CURRENT REPORTPursuant to Section 13 or 15(d)of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 25, 2026 Firefly Aerospace Inc.(Exact name of registrant as specified in its charter) 001-42789(CommissionFile Number) 1320 Arrow Point Drive, #109Cedar Park, Texas(Address of principal executive offices) Registrant’s telephone number, including area code: (512) 893-5570 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 thefollowing 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 Section12(b) of the Act: 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 thischapter) 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 anynew or revised financial accounting standards provided pursuant to Section13(a) of the Exchange Act.☐ Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; CompensatoryArrangements of Certain Officers. On February25, 2026, the Compensation Committee (the “Committee”) of the Board of Directors of Firefly Aerospace Inc. (the “Company”)adopted and approved the Firefly Aerospace Inc. Executive Severance Plan (the “Plan”). The Plan is intended to provide a standardized framework forthe payment of severance and other benefits to eligible officers and management employees designated by the Committee. Severance and other benefitsprovided for under the Plan apply in addition to (but without duplication of) any severance benefits provided under an eligible employee’s employmentagreement or offer letter with the Company. The Company’s executive officers will commence participation in the Plan upon executing and returning aparticipation agreement as provided under the Plan. The Plan provides a participating executive officer with the following severance payments in the event the executive officer’s employment withthe Company is terminated by the Company without “Cause” (as defined in the Plan and other than a termination due to the executive officer’s death or“Disability” (as defined in the Plan)) or due to the