Filed Pursuant to Rule 424(b)(3)
Registration No. 333-288796
PROSPECTUS SUPPLEMENT NO. 4
(TO PROSPECTUS DATED SEPTEMBER 19, 2025)
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 or amended from time to time, the “Prospectus”) of Rubico Inc.
(the “Company”), which forms a part of the Company’s Registration Statement 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 the information contained in the Company’s Report on Form 6-K, furnished to the U.S. Securities
and Exchange Commission (the “Commission”) on November 20, 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 by reference to the Prospectus except to the extent that the information in
this Prospectus Supplement supersedes the information contained in the Prospectus.
This Prospectus Supplement is not complete without,
and may not be delivered or utilized except in connection with, the Prospectus, 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 Prospectus for 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 or determined if this prospectus is truthful or complete. Any representation
to the contrary is a criminal offense.
The date of this prospectus supplement is November 20, 2025.
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 UNDER
THE SECURITIES EXCHANGE ACT OF 1934
For the month of November 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 cover
of Form 20-F or Form 40-F:
Form 20-F ☒ Form 40-F ☐
INFORMATION CONTAINED IN THIS FORM 6-K REPORT
As of November 19, 2025, Rubico Inc. (the “Company”) had 60,788,087
common shares, par value $0.01 per share (the “Common Shares”), issued and outstanding, which included Common Shares issued
upon the exercise of the Class A Warrants to purchase one Common Share (the “Class A Warrants”) and warrants issued to Maxim
Group LLC (the “Representative Warrants”), following the Company’s recent public offering of Common Shares, Class A
Warrants and Representative Warrants.
As of November 19, 2025, 164,600 Class A Warrants remain outstanding and
no Representative Warrants remain outstanding. If all of the remaining outstanding Class A Warrants are exercised on a zero cash basis,
there will be an additional 658,400 Common Shares issued and outstanding. See our Current Report on Form 6-K filed with the U.S. Securities
and Exchange Commission (the “Commission”) on November 7, 2025 for a description of the terms of the Class A Warrants.
Cautionary Note Regarding Forward-Looking Statements
Matters discussed in this report on Form 6-K may constitute forward-looking
statements. The Private Securities Litigation Reform Act of 1995 provides safe harbor protections for forward-looking statements in order
to encourage companies to provide prospective information about their business. Forward-looking statements include statements concerning
plans, objectives, goals, strategies, future events or performance, and underlying assumptions and other statements, which are other than
statements of historical facts, including statements regarding the Common Shares and the Class A Warrants.
The Company desires to take advantage of the safe harbor provisions of
the 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,” and
similar 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 operating
trends, data contained in the Company’s records, and other data available from third parties. Although the Company believes that
these assumptions were reasonable when made, because these assumptions are inherently subject to significant uncertainties and contingencies
which are difficult or impossible to predict and are beyond the Company’s control, the Company cannot assure you that it will achieve
or accomplish these expectations, beliefs, or projections. Please see the Company’s filings with the Commission for a more complete
discussion of these and other risks and uncertainties. The information set forth herein speaks only as of the date hereof, and the Company
disclaims any intention or obligation to update any forward-looking statements as a result of developments occurring after the date of
this report.
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.
| |
Rubico Inc. |
| |
|
| Date: November 20, 2025 |
By: /s/ Nikolaos Papastratis |
| |
Nikolaos Papastratis |
| |
Chief Financial Officer |
