Rubico Inc美股招股说明书(2026-01-02版)

Up to 15,000,000 Common Shares 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. 333-288796), 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 December 31, 2025 (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 12 of the Prospectusfor a 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 December 31, 2025. 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 December 2025 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 Mega Yacht Acquisition As previously announced, on December 4, 2025, Rubico Inc. (the “Company,” “we” or “our”) entered into a letter of intent(the “Newbuilding LOI”) for the potential acquisition from Top Ships Inc. (the “Parent”) of a newbuilding mega yacht, the M/YSanlorenzo 1150Exp (the “Newbuilding Yacht”), with expected delivery in the second quarter of 2027. The Company made anadvance cash payment of $4.0 million that was credited against the acquisition price of the Newbuilding Yacht A special independentcommittee composed of independent members of the Board of Directors negotiated and approved the acquisition of the NewbuildingYacht under the Newbuilding LOI. On December 31, 2025, the Company entered into a purchase agreement (the “Newbuilding SPA”)to purchase Roman Explorer Inc., the company that will acquire ownership of the Newbuilding Yacht, for a purchase price of $38.0million payable in installments over a period of 300 days following the Company’s entry into the Newbuilding SPA. An initialinstallment payment of $15.5 million was made upon signing the Newbuilding SPA, with consummation of the purchase and sale ofthe shares of Roman Explorer Inc. expected to take place no later than March 31, 2026. Under certain circumstances the Parent candemand the payment of installments in the form of newly-issued Series E Perpetual Convertible Preferred Shares (the “Series EPreferred Shares”). For a description of the Series E Preferred Shares, see the section of this Report titled “—Description of Series EPerpetual Convertible Preferred Shares.” Further, the form of Statement of Designation of the Series E Preferred Shares is appended tothe Newbuilding SPA, which is filed as an exhibit hereto. Remaining installments payable to the shipyard as per the relevantnewbuilding contract amount to approximately $41.5 million (or €35.5 million) payable up to May 2027. Supplemental Risk Factors The following should be read in conjunction with the risk factors previously disclosed in our registration statement on Form 20-Ffiled with the Commission on June 4, 2025. Delays or defaults by the shipyards in the construction of any newbuildings could increase our expenses and diminish our netincome and cash flows. As of the date of this report, we do not have any contracts for newbuilding vessels. We may enter into contracts for newbuildingvessels in the future. Vessel construction projects are generally subject to risks of delay that are inherent in any large constructionproject, which may be caused by numerous factors, including shortages of equipment, materials or skilled labor, unscheduled delays inthe delivery of ordered materials and equipment or shipyard construction, failur