Firefly Aerospace Inc美股招股说明书(2026-04-03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 Current Report on Form 8-K, filed with the Securitiesand Exchange Commission on April3, 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 April2, 2026, the closing price of our Common Stock was$32.93 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 April3, 2026. UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 FORM 8-K CURRENT REPORTPursuant to Section13 OR 15(d)of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April2, 2026 Firefly Aerospace Inc.(Exact name of registrant as specified in its charter) 001-42789(CommissionFile Number) Registrant’s telephone number, including area code: (512) 893-5570 1320 Arrow Point Drive, #109, Cedar Park, Texas 78613(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.☐ Item 1.01.Entry into a Material Definitive Agreement. Amendment to Credit Agreement On April3, 2026, Firefly Aerospace Inc. (the “Company”) entered into an amendment (the “Amendment”) to its Credit Agreement, dated as of August8,2025, by and among the Company, the other loan parties thereto, the lenders and issuing banks party thereto, and Wells Fargo Bank, NationalAssociation, as administrative agent (as so amended, the “Credit Agreement”). The Amendment, among other things, increased the existing commitments under the senior secured revolving credit facility (the “Revolving CreditFacility”) provided under the Credit Agreement by $45million, for a total aggregate principal amount of $305million. The Amendment also increasedthe interest spread applicable to the loans under the Revolving Credit Facility by 0.25%. After giving effect to the Amendment, the loans under theRevolving Credit Facility bear interest at a variable rate per annum equal to, at the Company’s option, either (a)term SOFR plus a 3.25% spread or(b)an alternative base rate (as set forth in the Credit Agreement) plus a 2.25% spread. A commitment fee of 0.375% per annum also applies on unusedcommitments under the Revolving Credit Facility. The Revolving Credit Facility ma