Rubico Inc美股招股说明书(2026-01-13版)

75,000 Common SharesOffered by the Selling Shareholders RUBICO INC. This is a supplement (the “Prospectus Supplement”) to the prospectus, dated September 19, 2025 (as supplemented oramended from time to time, the “Prospectus”) of Rubico Inc. (the “Company”), which forms a part of the Company’s RegistrationStatement on Form F-1 (Registration No. 333-289552), as amended from time to time. This Prospectus Supplement is being filed to update and supplement the information included in the Prospectus with theinformation contained in the Company’s Report on Form 6-K, furnished to the U.S. Securities and Exchange Commission (the“Commission”) on January 13, 2026 (the “Form 6-K”). Accordingly, the Form 6-K is attached to this Prospectus Supplement. This Prospectus Supplement should be read in conjunction with, and delivered with, the Prospectus and is qualified byreference to the Prospectus except to the extent that the information in this Prospectus Supplement supersedes the informationcontained in the Prospectus. This Prospectus Supplement is not complete without, and may not be delivered or utilized except in connection with, theProspectus, including any amendments or supplements to it. Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page 8 of the Prospectus fora discussion of information that should be considered in connection with an investment in our securities. Neither the Commission nor any state securities commission has approved or disapproved of these securities ordetermined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. The date of this prospectus supplement is January 13, 2026. UNITED STATES SECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 FORM 6-K REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13A-16 OR 15D-16 UNDER THE SECURITIESEXCHANGE ACT OF 1934 For the month of January 2026 Commission File Number: 001-42684 (Translation of registrant’s name into English) 20 Iouliou Kaisara Str19002 PaianiaAthens, Greece(Address of principal executive office) Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F: Form 20-F☒Form 40-F☐ INFORMATION CONTAINED IN THIS FORM 6-K REPORT Public Offering On January 12, 2026, Rubico Inc. (“we” or the “Company”), closed a public offering (the “Offering”) of 6,666,666 units (“Units”),each Unit consisting of one share of our common stock, par value $0.01 per share (“Common Shares”) (or one pre-funded warrant inlieu thereof, the “Pre-funded Warrant”) and one and one-half Class B Warrant (each, a “Class B Warrant”). Each Class B Warrant isexercisable to purchase one Common Share at a public offering price of $0.60 per Unit, subject to customary adjustments. In addition, we agreed to issue to Maxim Group LLC, the sole placement agent (the “Placement Agent” ) warrants to purchase anumber of Common Shares equal to 5.0% of the total number of Common Shares and Pre-funded Warrants sold in the Offering(the“Placement Agent Warrants”). Placement Agent Warrants to purchase 333,333 Common Shares were issued in connection with theclosing of the Offering. The Placement Agent Warrants have substantially similar terms as the Class B Warrants issued in the Offering. The Offering was made pursuant to a registration statement on Form F-1, as amended (File No. 333-292077), filed with the Securitiesand Exchange Commission (the “Commission”), which became effective with the Commission on January 9, 2026. The aggregate gross proceeds to the Company from the Offering, before deducting Placement Agent fees and other expenses payableby the Company, were approximately $4.0 million. On January 9, 2026, the Company released a press release furnished herewith as Exhibit 99.1, announcing the pricing of the Offering. Class B Warrants and Pre-funded Warrants The following summary of certain terms and provisions of the Warrants is not complete and is subject to, and qualified in its entiretyby, the provisions of the form of Warrant furnished as an exhibit to this report. Exercisability.The Class B Warrants are immediately exercisable at any time after their issuance and at any time up to the datethat is five years after their issuance. The Pre-funded Warrants are exercisable at any time after their original issuance until they areexercised in full. Each of the Class B Warrants and Pre-funded Warrants will be exercisable, at the option of each holder, in whole orin part by delivering to us a duly executed exercise notice with payment in full in immediately available funds for the number ofCommon Shares purchased upon such exercise (except in the case of a cashless exercise, as discussed below). We may be required topay certain amounts as liquidated damages as specified in the Class B Warrants and Pre-funded Warrants in the event we do not deliverCommon Shares upon exercise of the Class B Warrants and Pre-funded Warr