UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13A-16 OR 15D-16 UNDERTHE

SECURITIES EXCHANGE ACT OF 1934

For the month of August 2025

Commission File Number: 001-42684

RUBICO INC.

(Translation of registrant’s name into English)

20 Iouliou Kaisara Str

19002 Paiania

Athens, Greece

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under coverof Form 20-F or Form 40-F:

Form 20-F ☒ Form 40-F ☐

INFORMATION CONTAINED IN THIS FORM 6-K REPORT

Rubico Inc. (the “Company” or “Rubico”) (Nasdaq:RUBI) announced today that it has entered into two sale and leaseback financing agreements with a major Chinese financier for the refinancingof two 157,000 dwt Suezmax tankers, the M/Ts Eco West Coast and Eco Malibu (expected to be concluded during December 2025).The closing of these financing agreements is subject to conditions set forth in the relevant agreements.

Total proceeds from the two financing agreements will amount to $84.0 million,approximately $73.4 million of which will be used to repay the existing financing facilities for the two vessels and the remaining balancewill be used for general working capital purposes.

The financing agreements have durations of ten years and provide continuousoptions, after the first year, to buy back the vessels at purchase prices stipulated in the agreements.

Under the terms of the financing agreements, the Company will bareboatcharter back the vessels for a period of ten years at bareboat hire rates of $2.3 million per annum, plusinterest based on Term SOFR plus a margin of 2.10% per annum for the Eco Malibu, and an amortization schedule of $2.2 millionper annum, plus interest based on Term SOFR plus a margin of 1.95% per annum for the EcoWest Coast. At the end of the ten-year period, the Company has an obligation to buy back the vessels for $19.0 million for the EcoMalibu and $20.0 million for the Eco West Coast.

The financing agreements contain customary covenants and event of defaultclauses, including cross-default provisions and restrictive covenants and performance requirements including (i) a ratio of total netdebt to the aggregate market value of the Company’s fleet, current or future, of no more than 85% and (ii) minimum free liquidityof $0.50 million for the Eco Malibu and $0.40 million for the Eco West Coast.

Concurrently with entry into these financing agreements, Rubico Inc. andTOP Ships Inc. provided a guarantee of the obligations of Rubico Inc.’s vessel-owning subsidiaries under the respective financingagreements. The financing agreements contain cross-default provisions which would be triggered by a default under similar financing agreementsentered into by TOP Ships Inc. with the same major Chinese financier in an aggregate amount of $207.0 million.

Cautionary Note Regarding Forward-Looking Statements

Matters discussed in this press release may constitute forward-lookingstatements. The Private Securities Litigation Reform Act of 1995 provides safe harbor protections for forward-looking statements in orderto encourage companies to provide prospective information about their business. Forward-looking statements include statements concerningplans, objectives, goals, strategies, future events or performance, and underlying assumptions and other statements, which are other thanstatements of historical facts, including statements regarding the entry into and performance under the sale and leaseback financing agreements.

The Company desires to take advantage of the safe harbor provisions ofthe Private Securities Litigation Reform Act of 1995 and is including this cautionary statement in connection with this safe harbor legislation.The words “believe,” “anticipate,” “intends,” “estimate,” “forecast,” “project,”“plan,” “potential,” “may,” “should,” “expect,” “pending,” andsimilar expressions identify forward-looking statements. The forward-looking statements in this report are based upon various assumptions,many of which are based, in turn, upon further assumptions, including, without limitation, management's examination of historical operatingtrends, data contained in the Company’s records, and other data available from third parties. Although the Company believes thatthese assumptions were reasonable when made, because these assumptions are inherently subject to significant uncertainties and contingencieswhich are difficult or impossible to predict and are beyond the Company’s control, the Company cannot assure you that it will achieveor accomplish these expectations, beliefs, or projections. Please see the Company’s filings with the Securities and Exchange Commissionfor a more complete discussion of these and other risks and uncertainties. The information set forth herein speaks only as of the datehereof, and the Company disclaims any intention or obligation to update any forward-looking statements as a result of developmentsoccurring after the date of this communication.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended,the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.