As filed with the Securities and Exchange Commission on July 1, 2026

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM F-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

RUBICO INC.

(Exact name of registrant as specified in its charter)

N.A.

(Translation of Registrant’s name into English)

Rubico Inc.

20 Iouliou Kaisara Str,

19002 Paiania, Athens, Greece

Tel: + 30 210 812 8107

(Address and telephone number of Registrant’s principal executive offices)

With copy to:

Will Vogel

Watson Farley & Williams LLP

120 West 45^th Street

New York, New York 10019

+1 (212) 922-2200 (telephone number)

+1 (212) 922-1512 (facsimile number)

Will Vogel

Watson Farley & Williams LLP

120 West 45^th Street

New York, New York 10019

+1 (212) 922-2200 (telephone number)

+1 (212) 922-1512 (facsimile number)

(Name, address, and telephone number of agent for service)

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective as determined by market conditions and other factors.

If any of the securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.  ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a registration statement pursuant to General Instruction I.C. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.  ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.C. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ☐

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933.

Emerging growth company ☒

If an emerging growth company that prepares its financial statements in accordance with U.S. GAAP, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards† provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☒

† The term “new or revised financial accounting standard” refers to any update issued by the Financial Accounting Standards Board to its Accounting Standards Codification after April 5, 2012.

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We and the Selling Shareholders may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED July 1, 2026

PRELIMINARY PROSPECTUS

$200,000,000

Common Shares, Preferred Shares, Debt Securities,

Warrants, Purchase Contracts, Rights, Depositary Shares and Units

and

631,575 Common Shares Issuable upon Exercise of Warrants and Offered by the Selling Shareholders

Rubico Inc.

Through this prospectus we may periodically offer our:

We may also offer securities of the types listed above (together, the “Primary Offering Securities”) that are convertible or exchangeable into one or more of the securities listed above.

The aggregate offering price of the above securities issued under this prospectus may not exceed $200,000,000. The securities issued under this prospectus may be offered directly or through underwriters, agents or dealers. The names of any underwriters, agents or dealers will be included in a supplement to this prospectus.

The prices and other terms of the above securities that we will offer will be determined at the time of their offering and will be described in a supplement to this prospectus.

In addition, this prospectus relates to the resale, from time to time, by the selling shareholders identified in this prospectus under the caption “Selling Shareholders,” (the “Selling Shareholders”), of up to 631,575 of our common shares, par value $0.01 per share, including related preferred stock purchase rights (the “Secondary Offering Securities”), issuable upon exercise of our outstanding Class D Warrants to purchase common shares issued on June 26, 2026 (the “Class D Warrants”). The Class D Warrants were issued by us in a private placement under Section 4(a)(2) of the Securities Act pursuant to a letter agreement dated June 12, 2026 (the “Private Placement Transaction”).

We will receive proceeds from the issuance and sale of any Primary Offering Securities. We will not receive proceeds from the sale of Secondary Offering Securities by the Selling Shareholders.

Our common shares are currently listed on the Nasdaq Capital Market (“Nasdaq”) under the symbol “RUBI”.

The aggregate market value of our outstanding common shares held by non-affiliates as of June 30, 2026 is approximately $ 3,285,063, based on 604,984 common shares held by non-affiliates, and a closing price of our common shares on Nasdaq of $5.43 on June 30, 2026. As of the date hereof, we have not sold any securities pursuant to General Instruction I.B.5 of Form F-3 during the period of twelve calendar months immediately prior to, and including, the date hereof.

Investing in our securities involves a high degree of risk. See “Risk Factors” below, beginning on page 9, and the other risk factors contained in any applicable prospectus supplement and in the documents incorporated by reference herein or therein.

Neither the U.S. Securities and Exchange 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 is                             , 2026.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we have filed with the U.S. Securities and Exchange Commission (the “SEC” or the “Commission”), using a shelf registration process. Under the shelf registration process, we may sell common shares (including related preferred stock purchase rights), shares of preferred stock, debt securities, warrants, purchase contracts, rights, depositary shares and units described in this prospectus from time to time in one or more offerings up to a total dollar amount of $200,000,000, and we may issue common shares pursuant to the terms of certain of our outstanding warrants. Additionally, the Selling Shareholders may also offer and sell their respective common shares described in this prospectus in one or more offerings. This prospectus only provides you with a general description of the securities that we and the Selling Shareholders may offer. Each time we or the Selling Shareholders offer securities, we will provide you with a supplement to this prospectus that will describe the specific information about the securities being offered and the specific terms of that offering. The prospectus supplement may also add, update or change the information contained in this prospectus. If there is any inconsistency between the information in this prospectus and any prospectus supplement, you should rely on the prospectus supplement. Before purchasing any securities, you should read carefully both this prospectus and any prospectus supplement, together with the additional information described below.

This prospectus and any prospectus supplement are part of a registration statement we filed with the SEC and do not contain all the information in such registration statement. Forms of the indentures and other documents establishing the terms of the offered securities are filed as exhibits to the registration statement of which this prospectus forms a part. Statements in this prospectus or any prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. For further information about us or the securities offered hereby, you should refer to the registration statement of which this prospectus forms a part, which you can obtain from the SEC as described below under the section entitled “Where You Can Find More Information”.

The Selling Shareholders may offer and sell or otherwise dispose of their common shares described in this prospectus from time to time through public or private transactions at prevailing market prices, at prices related to prevailing market prices or at privately negotiated prices. The Selling Shareholders will bear all commissions and discounts, if any, attributable to the sales of their common shares. We will bear all other costs, expenses and fees in connection with the registration of the Selling Shareholders’ common shares. See “Plan of Distribution” for more information about how the Selling Shareholder may sell or dispose of their common shares.

You should rely only on the information contained or incorporated by reference in this prospectus and in any prospectus supplement. We have not and the Selling Shareholders have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We and the Selling Shareholders will not make an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and the applicable supplement to this prospectus is accurate as of the date on its respective cover, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, unless we indicate otherwise. Our business, financial condition, results of operations and prospects may have changed since those dates.

CAUTIONARY STATEMENT REGARDING 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. We desire to take advantage of the safe harbor provisions of the Private Securities Litigation Reform Act of 1995 and are including this cautionary statement in connection therewith. Forward-looking statements include, but are not limited to, statements regarding our or our management's expectations, hopes, beliefs, intentions or strategies regarding the future and other statements that are other than statements of historical fact. In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking.

The forward-looking statements in this prospectus and incorporated by reference herein 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 our records and other data available from third parties. Although we believe 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 our control, we cannot assure you that we will achieve or accomplish these expectations, beliefs or projections. As a result, you are cautioned not to rely on any forward-looking statements.

Many of these statements are based on our assumptions about factors that are beyond our ability to control or predict and are subject to risks and uncertainties that are described more fully in “Item 3. Key Information—D. Risk Factors” of our Annual Report on Form 20-F for the year ended December 31, 2025, which is incorporated by reference herein. Any of these factors or a combination of these factors could materially affect our future results of operations and the ultimate accuracy of the forward-looking statements. In addition to these important factors and matters discussed elsewhere herein and in the documents incorporated by reference herein, important factors that, in our view, could cause actual results to differ materially from those discussed in the forward-looking statements include, among other things:

Should one or more of the foregoing risks or uncertainties materialize, or should any of our assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. Consequently, there can be no assurance that actual results or developments anticipated by us will be realized or, even if substantially realized, that they will have the expected consequences to, or effects on, us. Given these uncertainties, prospective investors are cautioned not to place undue reliance on such forward-looking statements.

We undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable laws. If one or more forward-looking statements are updated, no inference should be drawn that additional updates will be made with respect to those or other forward-looking statements.

SERVICE OF PROCESS AND ENFORCEABILITY OF CIVIL LIABILITIES

We are a Marshall Islands corporation and our principal executive office is located outside of the United States in Athens, Greece.

Most of our directors and officers and those of our subsidiaries are residents of countries other than the United States. Substantially all of our and our subsidiaries’ assets and a substantial portion of the assets of our directors and officers are located outside the United States. As a result, it may be difficult or impossible for United States investors to effect service of process within the United States upon us, our directors or officers, our subsidiaries or to realize against us or them judgments obtained in United States courts, including judgments predicated upon the civil liability provisions of the securities laws of the United States or any state in the United States.

In addition, there is uncertainty as to whether the courts of the Marshall Islands would (1) recognize or enforce against us, or our directors, or officers, judgments of courts of the United States based on civil liability provisions of applicable U.S. federal and state securities laws; or (2) impose liabilities against us or our directors and officers in original actions brought in the Marshall Islands, based on these laws.

SUMMARY

This section summarizes certain of the information that is contained in this prospectus or the documents incorporated by reference herein, and this summary is qualified in its entirety by that more detailed information. This summary may not contain all of the information that may be important to you. We urge you to carefully read this entire prospectus and the documents incorporated by reference herein, including our financial statements and the related notes and the information in the section entitled “Item 5. Operating and Financial Review and Prospects” in our Annual Report on Form 20-F for the year ended December 31, 2025, which is incorporated by reference herein. As an investor or prospective investor, you should review carefully the more detailed information that appears later in this prospectus and the information incorporated by reference in this prospectus, including the section entitled “Risk Factors” herein. In addition, certain statements include forward-looking information that involves risks and uncertainties. See “Cautionary Statement Regarding Forward-Looking Statements” in this prospectus.

Unless otherwise indicated, references in this prospectus to “Rubico,” the “Company,” “we,” “our,” and “us,” refer to Rubico Inc. or any one or more of its subsidiaries, or to such entities collectively. References in this registration statement to the “Former Parent” refer to Top Ships Inc. References to our “Fleet Manager” or “CSI” are to Central Shipping Inc., a related party of our Former Parent and us, which performs the day-to-day management of our fleet.

Unless otherwise indicated, references to “U.S. dollars,” “dollars,” “USD” and “$” in this prospectus are to the lawful currency of the United States of America. We use the term “deadweight tons”, or “dwt”, expressed in metric tons, each of which is equivalent to 1,000 kilograms, in describing the size of vessels. We use the term “fleet” in describing our tanker vessels to the exclusion of any yachts that may be owned by us or purchased by us in the future.

Further, unless otherwise indicated, references to our common shares and per share amounts, including the number of common shares issuable upon exercise of warrants and the exercise price per common share, are adjusted to reflect the consolidation of our common shares through the one-for-thirty reverse stock split of our issued and outstanding common shares that became effective on December 2, 2025, the one-for-seven-and-eight-tenths reverse stock split of our issued and outstanding common shares that became effective on February 12, 2026, the one-for-ten reverse stock split of our issued and outstanding common shares that became effective on April 9, 2026, and the one-for-twenty-five reverse stock split of our issued and outstanding common shares that became effective on June 26, 2026.

Capitalized terms used but not defined in this prospectus shall have the meanings ascribed to them in our most recent Annual Report on Form 20-F, which was filed with the Commission on March 23, 2026.

Our Company

We are a global provider of shipping transportation services. We specialize in the ownership of vessels. The vessels initially comprising our fleet and each of the vessels we may acquire in the future is or will be owned through a separate wholly owned subsidiary.

We are an international owner and operator of two modern, fuel efficient eco, 157,000 dwt Suezmax tankers, the M/T Eco Malibu with an age of 5.1 years and the M/T Eco West Coast with an age of 5.3 years, each focusing on the transportation of crude oil.

We also have two newbuilding contracts, one for a 47,499 dwt chemical/product oil carrier and one for the M/Y Sanlorenzo 1150Exp, a 60 meters megayacht.

We were incorporated by the Former Parent under the laws of the Republic of the Marshall Islands on August 11, 2022 to serve as the holding company for two of its vessel-owning subsidiaries, Athenean Empire Inc. (the “Athenean Rubico Predecessor” or “Athenean”) and Roman Empire Inc. (the “Roman Rubico Predecessor” or “Roman” and, together with the Athenean Rubico Predecessor, the “Rubico Predecessor”) that were contributed to us by the Former Parent in connection with the distribution of our issued and outstanding common shares (including the related preferred stock purchase rights), to the Former Parent’s shareholders and warrant holders (the “Spin-Off”).

Chartering of our Fleet

We intend to expand our fleet into other seaborne transportation sectors depending on available opportunities, opportunistically considering further expansion into other crude or product oil tanker vessels as well as diversification into other sectors related to seaborne transportation of goods or passengers, including recreational transportation, depending on our assessment of market conditions and available opportunities at the time when an acquisition is possible. Our targets may include newbuilding vessels or vessels from the secondhand market, including acquisitions from unrelated third parties, the Former Parent or other related parties.

Management of our Company and our Fleet

Prior to the consummation of the Spin-Off, we entered into a letter agreement (the “CSI Letter Agreement”) with our Fleet Manager, a related party affiliated with the family of Mr. Evangelos J. Pistiolis, and our controlling shareholder, is a trust established for the benefit of certain family members of Mr. Evangelos J. Pistiolis, which detailed the terms on which any vessels we may acquire will be managed. Both Athenean and Roman have entered into management agreements with our Fleet Manager on May 28, 2020 and on March 18, 2026, Roman Shark IX Inc., a subsidiary of the Company entered into a management agreement with our Fleet Manager (each a “Management Agreement” and, together, “the “Management Agreements”). Both the Management Agreements and the CSI Letter Agreement can only be terminated subject to an eighteen-month advance notice, subject to a termination fee equal to twelve months of fees payable under the CSI Letter Agreement or each of the Management Agreements.

Pursuant to the CSI Letter Agreement as well as the Management Agreements, we currently pay a management fee of $670 per day per vessel for the provision of technical, commercial, operation, insurance, bunkering and crew management, commencing three months before the vessel is scheduled to be delivered by the shipyard. In addition, the Management Agreements and the CSI Letter Agreement provide for payment to our Fleet Manager of: (i) $609 per day for superintendent visits plus actual expenses; (ii) a chartering commission of 1.25% on all freight, hire and demurrage revenues; (iii) a commission of 1.00% on all gross vessel sale proceeds or the purchase price paid for vessels, (iv) in the case of a vessel under construction, a 1.00% of commission denoted as “Newbuilding vessels monitoring fee” that is payable as follows: 25% of the commission on the purchase of the newbuilding construction contract, 25% of the commission on the steel cutting of the newbuilding vessel, 25% of the commission on launching of the newbuilding vessel and 25% of the commission on the delivery of the newbuilding vessel to the Company (“steel cutting” and “launching” are newbuilding vessel construction milestones, evidenced by notices received by the shipyard) and (v) a financing fee of 0.2% on derivative agreements and loan financing or refinancing. Our Fleet Manager will also perform supervision services for any newbuilding vessel we may acquire while the vessel is under construction, for which we will pay our Fleet Manager the actual cost of the supervision services plus a fee of 7% of such supervision services.

Our Fleet Manager provides, at cost, all accounting, reporting and administrative services. Finally, the Management Agreements and the CSI Letter Agreement provide for a performance incentive fee for the provision of management services to be determined at the discretion of our Board of Directors (the “Board of Directors” or the “Board”). The Management Agreements and the CSI Letter Agreement have an initial term of five years, after which they will continue to be in effect until terminated by either party subject to an eighteen-month advance notice of termination. Pursuant to the terms of the Management Agreements and the CSI Letter Agreement, all fees payable to our Fleet Manager are adjusted annually according to the U.S. Consumer Price Index (“CPI”) of the previous year and if CPI is less than 2% then a 2% increase is effected and if CPI is more than 5%, then a 5% increase is effected.

For further information, please see “Major Shareholders and Related Party Transactions” in our most recent Annual Report on Form 20-F.

Our Competitive Strengths

Opportunity for growth. We believe we will be well positioned to opportunistically expand and maximize our current fleet due to competitive cost structure, strong customer relationships and experienced management team.

Demonstrated access to financing. We believe that we are well placed to take advantage of business opportunities due to the Fleet Manager’s operational platform, which we aim to leverage, along with our Fleet Manager’s demonstrated access to financing at the Former Parent. We believe that our ability to access financing will continue to allow us to capture additional market opportunities when they arise.

Our Fleet Manager’s commercial relationships, reputation and track record. We believe that our Fleet Manager’s network of commercial relationships and reputation and track record in building shipping fleets should provide us with access to attractive acquisition, chartering and vessel financing opportunities.

Modern, Fuel Efficient, Scrubber Fitted Fleet. Our vessels have the latest-generation, fuel efficient design and specifications. We believe that modern, fuel-efficient vessels like ours command higher charter rates than conventional vessels.

Our Business Strategies

Opportunistic and sector-agnostic vessel acquisition strategy. We plan to exploit opportunities in any sector related to seaborne transportation of goods or passengers, including recreational transportation that provides an attractive demand and supply profile as well as a positive market outlook in the medium to long-term by acquiring vessels trading in this sector. The decision for entering a new sector will be based on robust fundamentals and thoughtful analysis of factors affecting both the demand side and the supply side, while the selection of the target vessel will be subject to strict qualitative criteria including the environmental performance and energy efficiency of the acquisition candidates.

Expand our fleet through accretive acquisitions. We intend to grow our current fleet through timely and selective acquisitions of additional vessels at attractive valuations. In evaluating acquisitions, we consider and analyze, among other things, our expectation of fundamental developments in the shipping industry, the level of liquidity in the resale and charter market, the vessel condition and technical specifications, the expected remaining useful life, as well as the overall strategic positioning of our fleet and customers. For vessels acquired with charters attached, we also consider the credit quality of the charterer and the duration and terms of the contracts in place. Based on our Fleet Manager’s successful track record, commercial expertise and reputation in the marketplace as well as our transparent and public corporate structure, we believe that we are well-positioned to source off-market opportunities to acquire secondhand vessels. As a result, we may be able to acquire vessels on terms more favorable than those we could obtain without access to these opportunities.

Access to attractive chartering opportunities. Our Fleet Manager has built relationships with many well-known charterers, which we believe is the result of its and our Former Parent’s reputation for reliable service, safety and dependability. Through a combination of fixed period time charters and spot charters, our Former Parent and Fleet Manager have historically provided services to many national, regional and international oil companies, charterers and oil traders, including Shell, BP, ExxonMobil, Petrobras, ConocoPhillips, Pemex, Hellenic Petroleum, Glencore, Clearlake, Vitol and Trafigura. We focus on the needs of our customers and intend to acquire tankers and upgrade our fleet based on the requirements and specifications of our charterers, which we believe will enable us to obtain repeat business from our customers.

Environmental, Social, Governance, or ESG, Practices: We actively manage a broad range of ESG initiatives, taking into consideration their expected impact on the sustainability of our business over time, and the potential impact of our business on society and the environment. Scrubber installations, Existing Vessel Design Index, or EEXI, upgrades, and Energy Saving Devices (“ESDs”) installations, weather routing, slow steaming, ballast and trim optimization during the ballast voyage legs, application of noise reduction designs and frequent propeller and hull cleaning policy constitute examples of the environmental practices our management team has deployed. Moreover, we pay considerable attention to our human resources both on our vessels, or vessels we may acquire and ashore, proven by a variety of practices, including, gender discrimination elimination, performance KPIs, worldwide training and medical insurance.

Recent and Other Developments Summary

On March 31, 2025, the Newbuilding Yacht SPA was consummated. As of the date of this prospectus, the $38.0 million Newbuilding Yacht consideration has been settled in full.

On April 9, 2026, we effected a one-for-ten reverse stock split of our common shares. There was no change in the number of our authorized common shares.

On April 20, 2026, we entered into a second common shares purchase agreement (the “2026 Equity Line Purchase Agreement”) and a registration rights agreement (the “2026 Equity Line Registration Rights Agreement”) with B. Riley Principal Capital II, LLC (“B. Riley”). Pursuant to the 2026 Equity Line Purchase Agreement, we have the right to sell to B. Riley, from time to time during the term of the 2026 Equity Line Purchase Agreement, up to $50,000,000 of our common shares, subject to certain limitations and conditions set forth in the 2026 Equity Line Purchase Agreement. Sales of our common shares pursuant to the 2026 Equity Line Purchase Agreement, and the timing of any sales, are solely at our option, and we are under no obligation to sell any securities to B. Riley under the 2026 Equity Line Purchase Agreement. In accordance with our obligations under the 2026 Equity Line Registration Rights Agreement, we have registered under the Securities Act of 1933, as amended (the “Securities Act”), the resale by B. Riley of common shares that we may, in our sole discretion, elect to sell to B. Riley in one or more transactions from time to time during the term of the 2026 Equity Line Purchase Agreement. Our right to cause B. Riley to purchase our common shares is subject to certain conditions set forth in the 2026 Equity Line Purchase Agreement.

On May 21, 2026, we closed a public offering (the “May 2026 Offering”) of 210,526 units, with each unit consisting of one common share (or one pre-funded warrant in lieu thereof (the “May 2026 Pre-funded Warrants”)) and 1.5 Class C Warrants (each, a “Class C Warrant”). Each Class C Warrant was exercisable to purchase one common share at a public offering price of $23.75 per Class C Warrant, subject to customary adjustments. We also agreed to issue to Maxim Group LLC (“Maxim”), who acted as placement agent in the May 2026 Offering, warrants to purchase a number of common shares equal to 5.0% of the total number of common shares and May 2026 Pre-funded Warrants sold in the May 2026 Offering (the “May 2026 Representative Warrants”). May 2026 Representative Warrants to purchase 10,526 Common Shares were issued in connection with the closing of the May 2026 Offering. The May 2026 Representative Warrants have substantially similar terms to the Class C Warrants. As of the date of this registration statement no pre-funded warrants remain outstanding. The aggregate gross proceeds to us from the May 2026 Offering, before deducting placement agent fees and other expenses payable by us, were $5.0 million.

On June 12, 2026, we entered into a warrant exercise inducement letter agreement (“Inducement Letter”) with the existing holders of all of the Company’s outstanding Class C Warrants issued on May 21, 2026, exercisable to purchase up to an aggregate of 315,789 of the Company’s common shares, pursuant to which the holders agreed to exercise all of the outstanding Class C Warrants at an exercise price reduced from $23.75 per share to $16.25 per share. The net proceeds of the exercise of the Class C Warrants to the Company, after deducting estimated expenses and fees, were approximately $4.8 million. In consideration for the immediate exercise of the Class C Warrants for cash, the exercising holders received Class D Warrants to purchase up to an aggregate of 631,575 Common Shares in the Private Placement Transaction. The Class D Warrants were issued on June 26, 2026, were immediately exercisable upon issuance at an exercise price of $16.25 per Common Share and will expire five years after issuance.

On June 26, 2026, we effected a one-for-twenty-five reverse stock split of our common shares. There was no change in the number of our authorized common shares.

Corporate Information

Rubico Inc. is a holding company existing under the laws of the Republic of the Marshall Islands. Our executive offices are currently located at 20 Iouliou Kaisara Str, 19002, Paiania, Athens, Greece and our telephone number is +30 210 812 8107. Our website is www.rubicoinc.com. The Commission maintains a website that contains reports, proxy and information statements, and other information that we file electronically at www.sec.gov. The information contained on, or that can be accessed through, these websites is not incorporated by reference herein and does not form part of this prospectus.

Formation Transactions

The operating vessels of our fleet were contributed to us by the Former Parent in connection with the Spin-Off.

The Spin-Off distribution occurred on August 1, 2025. The Spin-Off distribution was pro rata to the beneficial holders of the Former Parent’s outstanding common shares and to beneficial holders of the Former Parent’s outstanding common stock purchase warrants on an as-exercised basis to the extent such warrants contain anti-dilution provisions conferred an interest equivalent to the Spin-Off distribution, in each case as of June 16, 2025, the record date of the Spin-Off, so that such holders maintained the same proportionate interest (on a fully-diluted basis) in each respective class of shares of the Former Parent and of us both immediately before and immediately after the Spin-Off. In connection with the Spin-Off, the Former Parent distributed 100,000 Series D preferred shares (the “Series D Preferred Shares”) to the holder of the Series D perpetual preferred shares of the Former Parent. The Series D Preferred Shares distributed to the holder of the Series D perpetual preferred shares of the Former Parent were created to mirror the rights of the Series D perpetual preferred shares of the Former Parent. The holder of the Series D perpetual preferred shares of the Former Parent is the Lax Trust, which is an irrevocable trust established for the benefit of certain family members of the President, Chief Executive Officer and Director of the Former Parent, Mr. Evangelos Pistiolis. The Former Parent did not distribute the Series D Preferred Shares to its common shareholders in connection with the Spin-Off.

On June 23, 2025, in connection with the Spin-Off, Nasdaq approved the listing of our common shares under the symbol “RUBI.” The common shares began trading on Nasdaq on August 4, 2025, the Trading Day following the consummation of the Spin-Off.

Implications of Being a Foreign Private Issuer

As a non-U.S. company which qualifies as a “foreign private issuer” subject to reporting requirements under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), we are subject to different requirements under the U.S. securities laws than U.S. domestic issuers. See “Item 3. Key Information-D. Risk Factors-Risks Relating to Our Company-We are a ‘foreign private issuer,’ which could make our common shares less attractive to some investors or otherwise harm our stock price” in our most recent Annual Report on Form 20-F and “Where You Can Find More Information.”

Implications of Being an Emerging Growth Company

We qualify as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. An emerging growth company may take advantage of specified reduced reporting and other burdens that are otherwise applicable generally to public companies. These provisions include:

We may take advantage of these provisions until the end of the fiscal year following the fifth anniversary of the closing of this offering or such earlier time that we are no longer an emerging growth company. We will cease to be an emerging growth company if we have more than $1.235 billion in “total annual gross revenues” during the most recently completed fiscal year, or we have issued more than $1 billion in non-convertible debt in the past three years, or we become a “large accelerated filer”. For as long as we take advantage of the reduced reporting obligations, the information that we provide shareholders may be different from information provided by other public companies.

We are choosing to take advantage of these reduced burdens, save for the exemption from new or revised financial accounting standards applicable to public companies until such standards are also applicable to private companies. We are choosing to “opt out” of such extended transition period and will comply with new or revised accounting standards on the relevant dates on which adoption of such standards is required for non-emerging growth public companies. Section 107 of the JOBS Act provides that our decision to opt out of the extended transition period for complying with new or revised accounting standards is irrevocable.

The Securities We May Offer

We may use this prospectus to offer up to $200,000,000 of our:

We may also offer securities of the types listed above that are convertible or exchangeable into one or more of the securities listed above. A prospectus supplement will describe the specific types, amounts, prices, and detailed terms of any of these offered securities and may describe certain risks in addition to those set forth below associated with an investment in the securities. Terms used in the prospectus supplement will have the meanings described in this prospectus, unless otherwise specified.

RISK FACTORS

An investment in our securities involves a high degree of risk. Before making an investment in our securities, you should carefully consider all of the information included or incorporated by reference into this prospectus, including the risks described under the heading “Item 3. Key Information—D. Risk Factors” in our Annual Report on Form 20-F for the year ended December 31, 2025, which is incorporated by reference herein, and as updated by annual and other reports and documents we file with the SEC after the date of this prospectus and that are incorporated by reference herein. Please see the section of this prospectus entitled “Where You Can Find More Information.” The occurrence of one or more of those risk factors could adversely impact our business, financial condition or results of operations.

USE OF PROCEEDS

We intend to use the net proceeds from the sale of the Primary Offering Securities as set forth in any applicable prospectus supplement to this prospectus.

We will not receive any proceeds from the sale of the Secondary Offering Securities to be offered by the Selling Shareholders pursuant to this prospectus or, to the extent relevant, any applicable future prospectus.

CAPITALIZATION

The following table sets forth our capitalization and indebtedness as of December 31, 2025:

3.

Based on our audited consolidated financial statements of Rubico Inc.:

Expressed in thousands of U.S. dollars, except for share data

DILUTION

To the extent applicable, information about the amount by which the offering price per share of our securities issued pursuant to this prospectus exceeds the net tangible book value per share of our securities following such issuance will be included in a prospectus supplement.

DESCRIPTION OF CAPITAL STOCK

See “Item 10. Additional Information — B. Memorandum and Articles of Association” in our Annual Report on Form 20-F for the year ended December 31, 2025, incorporated by reference herein.

DESCRIPTION OF DEBT SECURITIES

We may offer and issue debt securities from time to time in one or more series, under one or more indentures, each dated as of a date on or prior to the issuance of the debt securities to which it relates, and pursuant to an applicable prospectus supplement. We may issue senior debt securities and subordinated debt securities pursuant to separate indentures, a senior indenture and a subordinated indenture, respectively, in each case between us and the trustee named in the indenture. We have filed forms of these documents as exhibits to the registration statement, of which this prospectus forms a part. We refer to any applicable prospectus supplement, amendment to the registration statement of which this prospectus forms a part, report we file with the SEC under the Exchange Act as “subsequent filings.” The senior indenture and the subordinated indenture, as amended or supplemented from time to time, are each referred to individually as an “indenture” and collectively as the “indentures.” Each indenture will be subject to and governed by the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”), and will be construed in accordance with and governed by the laws of the State of New York (without giving effect to any principles thereof relating to conflicts of law that would result in the application of the laws of any other jurisdiction) unless otherwise stated in the applicable prospectus supplement and indenture (or post-effective amendment hereto). Each indenture will contain the specific terms of any series of debt securities or provide that those terms must be set forth in or determined pursuant to, an authorizing resolution, as defined in the applicable prospectus supplement or a supplemental indenture, if any, relating to such series. Our debt securities may be convertible or exchangeable into any of our equity or other debt securities.

The following description sets forth certain general terms and provisions of the debt securities. The particular terms and provisions of the debt securities offered by any prospectus supplement, and the extent to which the general terms and provisions described below may apply to the offered debt securities, will be described in the applicable subsequent filings. The statements below are not complete and are subject to, and are qualified in their entirety by reference to, all of the provisions of the applicable indenture. The specific terms of any debt securities that we may offer, including any modifications of, or additions to, the general terms described below as well as any applicable material U.S. federal income tax considerations concerning the ownership of such debt securities will be described in the applicable prospectus supplement and indenture and, as applicable, supplemental indenture. Accordingly, for a complete description of the terms of a particular issue of debt securities, the general description of the debt securities set forth below should be read in conjunction with the applicable prospectus supplement and indenture, as amended or supplemented from time to time.

General

We expect that neither indenture will limit the amount of debt securities that may be issued. The debt securities may be issued in one or more series.

You should read the applicable indenture and subsequent filings relating to the particular series of debt securities for the following terms of the offered debt securities:

Subsequent filings may include additional terms not listed above. Unless otherwise indicated in subsequent filings with the SEC relating to the indenture, principal, premium and interest will be payable and the debt securities will be transferable at the corporate trust office of the applicable trustee. Unless other arrangements are made or set forth in subsequent filings or a supplemental indenture, principal, premium and interest will be paid by checks mailed to the registered holders at their registered addresses.

Unless otherwise indicated in subsequent filings with the SEC, the debt securities will be issued only in fully registered form without coupons, in denominations of $1,000 or any integral multiple thereof. No service charge will be made for any transfer or exchange of the debt securities, but we may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection with these debt securities.

Some or all of the debt securities may be issued as discounted debt securities, bearing no interest or interest at a rate which at the time of issuance is below market rates, to be sold at a substantial discount below the stated principal amount. United States federal income tax consequences and other special considerations applicable to any discounted securities will be described in subsequent filings with the SEC relating to those securities.

We refer you to the appliable subsequent filings for the particular terms and provisions of the debt securities offered by any prospectus supplement.

Senior Debt Securities

We may issue senior debt securities, which may be secured or unsecured, under the senior debt indenture. The senior debt securities will rank on an equal basis with all our other senior debt except subordinated debt. The senior debt securities will be effectively subordinated, however, to all of our secured debt to the extent of the value of the collateral securing such debt. We will disclose the amount of our debt in the prospectus supplement.

Subordinated Debt Securities

We may issue subordinated debt securities under a subordinated debt indenture. Subordinated debt would rank subordinate and junior in right of payment, to the extent set forth in the subordinated debt indenture, to all our senior debt.

Covenants

Any series of offered debt securities may have covenants in addition to or differing from those included in the applicable indenture which will be described in subsequent filings prepared in connection with the offering of such securities, limiting or restricting, among other things:

Modification of the Indentures

We expect that each indenture and the rights of the respective holders generally may be modified by us only with the consent of holders of not less than a majority in aggregate principal amount of the outstanding debt securities of all series under the respective indenture affected by the modification, taken together as a class. But we expect that no modification that:

Events of Default

We expect that each indenture will define an event of default for the debt securities of any series as being any one of the following events:

An event of default of one series of debt securities will not necessarily constitute an event of default with respect to any other series of debt securities.

There may be such other or different events of default as described in any applicable subsequent filing with respect to any class or series of offered debt securities.

We expect that under each indenture, in case an event of default occurs and continues for the debt securities of any series, the applicable trustee or the holders of not less than 25% in aggregate principal amount of the debt securities then outstanding of that series may declare the principal and accrued but unpaid interest of the debt securities of that series to be due and payable. Further, any event of default for the debt securities of any series which has been cured is expected to be permitted to be waived by the holders of a majority in aggregate principal amount of the debt securities of that series then outstanding.

We expect that each indenture will require us to file annually after debt securities are issued under that indenture with the applicable trustee a written statement signed by two of our officers as to the absence of material defaults under the terms of that indenture. We also expect that each indenture will provide that the applicable trustee may withhold notice to the holders of any default if it considers it in the interest of the holders to do so, except notice of a default in payment of principal, premium or interest.

Subject to the duties of the trustee in case an event of default occurs and continues, we expect that each indenture will provide that the trustee is under no obligation to exercise any of its rights or powers under that indenture at the request, order or direction of holders unless the holders have offered to the trustee reasonable indemnity. Subject to these provisions for indemnification and the rights of the trustee, each indenture is expected to provide that the holders of a majority in principal amount of the debt securities of any series then outstanding have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee as long as the exercise of that right does not conflict with any law or the indenture.

  Defeasance and Discharge

The terms of each indenture are expected to provide us with the option to be discharged from any and all obligations in respect of the debt securities issued thereunder upon the deposit with the trustee, in trust, of money or United States government obligations, or both, which through the payment of interest and principal in accordance with their terms will provide money in an amount sufficient to pay any installment of principal, premium and interest on, and any mandatory sinking fund payments in respect of, the debt securities on the stated maturity of the payments in accordance with the terms of the debt securities and the indenture governing the debt securities. We expect that this right may only be exercised if, among other things, we have received from, or there has been published by, the United States Internal Revenue Service a ruling to the effect that such a discharge will not be deemed, or result in, a taxable event with respect to holders. This discharge would not apply to our obligations to register the transfer or exchange of debt securities, to replace stolen, lost or mutilated debt securities, to maintain paying agencies and hold moneys for payment in trust.

Defeasance of Certain Covenants

We expect that the terms of the debt securities provide us with the right not to comply with specified covenants and that specified events of default described in a subsequent filing will not apply provided we deposit with the trustee money or U.S. government obligations, or both, which through the payment of interest and principal will provide money in an amount sufficient to pay any installment of principal, premium, and interest on, and any mandatory sinking fund payments in respect of, the debt securities on the stated maturity of such payments in accordance with the terms of the debt securities and the indenture governing such debt securities.

We expect that to exercise this right, we will also be required to deliver to the trustee an opinion of counsel to the effect that the deposit and related covenant defeasance should not cause the holders of such series to recognize income, gain or loss for United States federal income tax purposes.

A subsequent filing may further describe the provisions, if any, of any particular series of offered debt securities permitting a discharge defeasance.

Form of Debt Securities

Each debt security will be represented either by a certificate issued in definitive form to a particular investor or by one or more global securities representing the entire issuance of securities. Both certificated securities in definitive form and global securities may be issued either in registered form, where our obligation runs to the holder of the security named on the face of the security, or in bearer form, where our obligation runs to the bearer of the security.

Definitive securities name the owner or their nominee as the owner of the security, other than definitive bearer securities, which name the bearer as owner, and in order to transfer or exchange these securities or to receive payments other than interest or other interim payments, the owner or their nominee must physically deliver the securities to the trustee, registrar, paying agent or other agent, as applicable.

Global securities name a depositary or its nominee as the owner of the debt securities represented by these global securities, other than global bearer securities, which name the bearer as owner. The depositary maintains a computerized system that will reflect each investor’s beneficial ownership of the securities through an account maintained by the investor with its broker/dealer, bank, trust company or other representative, as we explain more fully below.

Global Securities

The debt securities of a series may be issued in whole or in part in the form of one or more global securities that will be deposited with, or on behalf of, a depository identified in an applicable subsequent filing and registered in the name of the depository or a nominee for the depository. In such a case, one or more global securities will be issued in a denomination or aggregate denominations equal to the portion of the aggregate principal amount of outstanding debt securities of the series to be represented by the global security or securities. Unless and until it is exchanged in whole or in part for debt securities in definitive certificated form, a global security may not be transferred except as a whole by the depository for the global security to a nominee of the depository or by a nominee of the depository to the depository or another nominee of the depository or by the depository or any nominee to a successor depository for that series or a nominee of the successor depository and except in the circumstances described in an applicable subsequent filing.

We refer you to applicable subsequent filings with respect to any deletions or additions or modifications from the description contained in this prospectus.

DESCRIPTION OF WARRANTS

We may issue warrants to purchase any of our debt or equity securities or other rights, including rights to receive payment in cash or securities based on the value, rate or price of one or more specified currencies, securities or indices, or any combination of the foregoing. Warrants may be issued independently or together with any other securities and may be attached to, or separate from, such securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a warrant agent. The terms of any warrants to be issued and a description of the material provisions of the applicable warrant agreement will be set forth in the applicable prospectus supplement. We expect that such terms will include, among others:

DESCRIPTION OF PURCHASE CONTRACTS

We may issue purchase contracts for the purchase or sale of debt or equity securities issued by us, a basket of such securities, an index or indices of such securities, or any combination of the above as specified in the applicable prospectus supplement; or currencies.

Each purchase contract will entitle the holder thereof to purchase or sell, and obligate us to sell or purchase, on specified dates, such securities or currencies at a specified purchase price, which may be based on a formula, all as set forth in the applicable prospectus supplement. Any purchase contracts we issue will be physically settled by delivery of the securities or, in the case of purchase contracts on underlying currencies, by delivering the underlying currencies, as set forth in the applicable prospectus supplement. The applicable prospectus supplement will also specify the methods by which the holders may purchase or sell such securities or currencies and any acceleration, cancellation or termination provisions, provisions relating to U.S. federal income tax considerations, if any, or other provisions relating to the settlement of a purchase contract.

The purchase contracts may require the holders thereof to secure their obligations in a specified manner to be described in the applicable prospectus supplement. Alternatively, purchase contracts may require holders to satisfy their obligations thereunder when the purchase contracts are issued. Our obligation to settle such pre-paid purchase contracts on the relevant settlement date may constitute indebtedness. Accordingly, pre-paid purchase contracts will be issued under either a senior indenture or subordinated indenture.

DESCRIPTION OF RIGHTS

We may issue rights to purchase our securities. These rights may be issued independently or together with any other security offered by this prospectus and may or may not be transferable by the shareholder receiving the rights in the rights offering. In connection with any rights offering, we may enter into a standby underwriting agreement with one or more underwriters pursuant to which the underwriter will purchase any securities that remain unsubscribed for upon completion of the rights offering.

The applicable prospectus supplement relating to any rights will describe the terms of the offered rights, including, where applicable, the following:

The description in the applicable prospectus supplement of any rights we offer will not necessarily be complete and will be qualified in its entirety by reference to the applicable rights certificate or rights agreement, which will be filed with the SEC if we offer rights. For more information on how you can obtain copies of any rights certificate or rights agreement if we offer rights, see “Where You Can Find More Information” of this prospectus. We urge you to read the applicable rights certificate, the applicable rights agreement and any applicable prospectus supplement in their entirety.

DESCRIPTION OF DEPOSITARY SHARES

We may issue fractional shares of preferred stock, rather than full shares of preferred stock. If we do so, we may issue receipts for depositary shares that each represent a fraction of a share of a particular series of preferred stock. A related prospectus supplement will indicate that fraction. The shares of preferred stock represented by depositary shares will be deposited under a depositary agreement between us and a bank or trust company that is selected by us, which we refer to as the “bank depositary.” Each owner of a depository share will be entitled to all the right, preferences and privileges of the preferred stock represented by the depositary share. The depositary share will be evidenced by depositary receipts issued pursuant to the depositary agreement. Depositary receipts will be distributed to those persons purchasing the fractional shares of preferred stock in accordance with the terms of the offering.

The forms of the depositary agreement and the depository receipts relating to any particular issue of depositary shares will be filed with the SEC each time we issue depositary shares, and any prospectus supplement relating to any particular depositary shares will describe, among other things, the following:

You should read the particular terms of any depositary shares and any depositary receipts that we offer and any deposit agreement relating to a particular series of preferred shares which will be described in more detail in a prospectus supplement. A copy of the form of deposit agreement, including the form of depositary receipt, will be filed with the SEC at the time of the offering and incorporated by reference into the registration statement of which this prospectus forms a part. You can obtain copies of these documents when they are filed by following the directions outlined in “Where You Can Find More Information.”

DESCRIPTION OF UNITS

As specified in the applicable prospectus supplement, we may issue units consisting of one or more of our depositary shares, rights, purchase contracts, warrants, debt securities, shares of preferred stock, common shares (including preferred stock purchase rights) or any combination of such securities. The applicable prospectus supplement will describe, to the extent applicable:

TAX CONSIDERATIONS

Our Annual Report on Form 20-F for the year ended December 31, 2025, which is incorporated by reference herein, as updated by annual and other reports and document we file with the SEC after the date of this prospectus and that are incorporated by reference herein, provides a discussion of the material U.S. federal income tax considerations and Marshall Islands tax considerations that may be relevant to prospective investors in our common shares. The applicable prospectus supplement may also contain information about any material U.S. federal income tax considerations and any material non-U.S. tax considerations relating to the securities covered by such prospectus supplement.

SELLING SHAREHOLDERS

This prospectus relates in part to the offering of up to 631,575 common shares that the Selling Shareholders may sell in one or more offerings upon exercise of some or all of the Class D Warrants that the Selling Shareholders have purchased from us in the Private Placement Transaction.

The selling shareholders listed below and their permitted transferees, pledgees or other successors may from time to time offer and sell any or all of the common shares set forth below pursuant to this prospectus. When we refer to the “Selling Shareholders” in this prospectus, we refer to the persons listed in the table below, and the pledgees, donees, transferees, assignees, successors and other permitted transferees that hold any of that Selling Shareholder’s interest in the common shares after the date of this prospectus.

The registration of these common shares does not mean that the Selling Shareholders will sell or otherwise dispose of all or any of those securities. The Selling Shareholders may sell or otherwise dispose of all, a portion or none of such common shares from time to time. We do not know the number of common shares, if any, that will be offered for sale or other disposition by any of the Selling Shareholders under this prospectus. The Selling Shareholders identified below may currently hold or acquire our common shares or warrants to purchase our common shares in addition to the Class C Warrants or the common shares registered hereby. In addition, the Selling Shareholders identified below may sell, transfer, assign or otherwise dispose of some or all of the common shares covered hereby in private placement transactions exempt from or not subject to the registration requirements of the Securities Act.

To our knowledge, the Selling Shareholders do not have nor have had within the past three years, any position, office or other material relationship with us or any of our predecessors or affiliates, other than their ownership of our common shares.

The following table sets forth certain information with respect to each Selling Shareholder, including (i) the common shares beneficially owned by the Selling Shareholder prior to this offering (including the common shares underlying the Class D Warrants), (ii) the number of common shares underlying the Class D Warrants and being offered by the Selling Shareholder pursuant to this prospectus and (iii) the Selling Shareholder’s beneficial ownership after completion of this offering, assuming that all of the common shares covered hereby (but none of the other common shares, if any, held by the Selling Shareholders) are sold.

We have prepared the following table based on information supplied to us by the Selling Shareholders on or prior to June 30, 2026, and we have not sought to verify such information. Ownership and percentage ownership are determined in accordance with the rules and regulations of the SEC regarding beneficial ownership and include voting or investment power with respect to common shares. This information does not necessarily indicate beneficial ownership for any other purpose. In computing the number of common shares beneficially owned by a Selling Shareholder and the percentage ownership of that Selling Shareholder, common shares underlying warrants held by that selling stockholder that are exercisable as of June 30, 2026, or exercisable within 60 days after June 30, 2026, are deemed outstanding. Such common shares, however, are not deemed outstanding for the purposes of computing the percentage ownership of any other person. The calculation of percentage of beneficial ownership is based on 605,012 common shares issued and outstanding as of June 30, 2026. The number of common shares owned prior to this offering and the number of common shares owned following this offering in the table below do not give effect to the beneficial ownership limitation contained in the Class D Warrants held by the Selling Shareholders, but the percentages in the table below do give effect to such beneficial ownership limitation.

(1) Applicable percentage ownership is based on 605,012 common shares outstanding as of June 30, 2026. The Class D Warrants are subject to a beneficial ownership limitation of 4.99%, which such limitation restricts each Selling Shareholder from exercising that portion of the Class D Warrants that would result in the relevant Selling Shareholder and its affiliates owning, after exercise, a number of shares of common stock in excess of the beneficial ownership limitation.

(2) Assumes the exercise of all Class D Warrants and the sale of all Secondary Offering Securities being registered pursuant to this registration statement.

(3) Anson Advisors Inc and Anson Funds Management LP, the Co-Investment Advisers of Anson Investments Master Fund LP (“AIMF”) and Anson East Master Fund LP (“AEMF”, and collective with AIMF, “ANSON”), hold voting and dispositive power over the shares of common stock held by ANSON. Tony Moore is the managing member of Anson Management GP LLC, which is the general partner of Anson Funds Management LP. Moez Kassam and Amin Nathoo are directors of Anson Advisors Inc. Mr. Moore, Mr. Kassam and Mr. Nathoo each disclaim beneficial ownership of these shares of common stock except to the extent of their pecuniary interest therein. The principal business address of ANSON is Maples Corporate Services Limited, PO Box 309, Ugland House, Grand Cayman, KY1-1104, Cayman Islands.

(4) Hudson Bay Master Fund Ltd. ("Hudson Bay"). Hudson Bay Capital Management LP, the investment manager of Hudson Bay, has voting and investment power over these securities. Sander Gerber is the managing member of Hudson Bay Capital GP LLC, which is the general partner of Hudson Bay Capital Management LP. Each of Hudson Bay and Sander Gerber disclaims beneficial ownership over these securities. The principal business address of Hudson Bay is c/o Hudson Bay Capital Management LP, 290 Harbor Dr., 3rd Floor, Stamford, CT 06902.

(5) The securities are directly held by Armistice Capital Master Fund Ltd., a Cayman Islands exempted company (the “Master Fund”), and may be deemed to be beneficially owned by: (i) Armistice Capital, LLC (“Armistice Capital”), as the investment manager of the Master Fund; and (ii) Steven Boyd, as the Managing Member of Armistice Capital. The warrants are subject to a beneficial ownership limitation of 4.99%, which such limitation restricts the Selling Shareholder from exercising that portion of the warrants that would result in the Selling Shareholder and its affiliates owning, after exercise, a number of shares of common stock in excess of the beneficial ownership limitation. The address of Armistice Capital Master Fund Ltd. is c/o Armistice Capital, LLC, 510 Madison Avenue, 7th Floor, New York, NY 10022.

(6) The shares of common stock are directly held by Funicular Funds, LP and may be deemed to be beneficially owned by Jacob Ma-Weaver, who has investment and dispositive power over the securities. The address of Funicular Funds, LP and Mr. Ma-Weaver is 601 California Street, Suite 1151, San Francisco, CA 94108.

PLAN OF DISTRIBUTION

We and the Selling Shareholders may sell or distribute the securities included in this prospectus through underwriters, through agents, to dealers, in private transactions, at market prices prevailing at the time of sale, at prices related to market prices, at a fixed price or prices subject to change, at varying prices determined at the time of sale (which may be above or below market prices prevailing at the time of sale) or at negotiated prices. The Selling Shareholders, which, as used herein, includes donees, pledgees, transferees, or other successors-in-interest selling common shares or interests in common shares received after the date of this prospectus from the Selling Shareholders as a gift, pledge, partnership distribution, or other non-sale related transfer, may, from time to time, sell, transfer, or otherwise dispose of any or all of their common shares on any stock exchange, market or trading facility on which the shares are traded or in private transactions.

 The Selling Shareholders will act independently of us in making decisions with respect to the timing, manner and size of each sale of the Secondary Offering Securities. The Selling Shareholders may, from time to time, pledge or grant a security interest in some or all of the common shares owned by such shareholder and, if he defaults in the performance of his secured obligations, the pledgees or secured parties may offer and sell the common shares, from time to time, under this prospectus, or under an amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act amending the list of Selling Shareholders to include the pledgee, transferee, or other successors in interest as Selling Shareholders under this prospectus. In addition, we and the Selling Shareholders may sell some or all of our securities included in this prospectus through:

In addition, we and the Selling Shareholders may enter into options or other types of transactions that require us to deliver our securities to a broker-dealer, who will then resell or transfer the securities under this prospectus. We may enter into hedging transactions with respect to our securities. For example, we and the Selling Shareholders may:

We and the Selling Shareholders may also sell securities under Rule 144 or any other exemption from registration under the Securities Act, if available, rather than under this prospectus.

We and the Selling Shareholders may enter into derivative transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from us in settlement of those derivatives to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and, if not identified in this prospectus, will be identified in the applicable prospectus supplement (or a post-effective amendment). In addition, we and the Selling Shareholders may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

Any broker-dealers or other persons acting on our or the Selling Shareholders’ behalf that participate with us in the distribution of the securities may be deemed to be underwriters and any commissions received or profit realized by them on the resale of the securities may be deemed to be underwriting discounts and commissions under the Securities Act. As of the date of this prospectus, neither we nor the Selling Shareholders are a party to any agreement, arrangement or understanding between any broker or dealer and us with respect to the offer or sale of the securities pursuant to this prospectus.

If a Selling Shareholder is deemed an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act, he will be subject to the prospectus delivery requirements of the Securities Act. We will make copies of this prospectus (as it may be amended from time to time) available to the Selling Shareholders for the purpose of satisfying the prospectus delivery requirements of the Securities Act.

In effecting sales, broker-dealers or agents engaged by the Selling Shareholder may arrange for other broker-dealers to participate. Broker-dealers or agents may receive commissions, discounts or concessions from the Selling Shareholder, in amounts to be negotiated immediately prior to the sale.

As of the date of this prospectus, we are not a party to any agreement, arrangement or understanding between any broker or dealer and us with respect to the offer or sale of securities pursuant to this prospectus.

At the time that any particular offering of securities is made, to the extent required by the Securities Act, a prospectus supplement will be distributed, setting forth the terms of the offering, including the aggregate number of securities being offered, the purchase price of the securities, the initial offering price of the securities, the names of any underwriters, dealers or agents, any discounts, commissions and other items constituting compensation from us and any discounts, commissions or concessions allowed or reallowed or paid to dealers. Furthermore, we, our executive officers, our directors and major shareholders may agree, subject to certain exemptions, that for a certain period from the date of the prospectus supplement under which the securities are offered, we and they will not, without the prior written consent of an underwriter, offer, sell, contract to sell, pledge or otherwise dispose of any of our common shares or any securities convertible into or exchangeable for common shares. However, an underwriter, in its sole discretion, may release any of the securities subject to these lock-up agreements at any time without notice. We expect an underwriter to exclude from these lock-up agreements securities exercised and/or sold pursuant to trading plans entered into by us pursuant to Rule 10b5-1 under the Exchange Act, that are in place at the time of an offering pursuant to this prospectus and any applicable prospectus supplement hereto that provide for periodic sales of our securities on the basis of parameters described in such trading plans.

The Selling Shareholders and any other person participating in a distribution of the common shares covered by this prospectus will be subject to the applicable provisions of the Exchange Act, and the rules and regulations thereunder, including Regulation M, which may limit the timing of purchases and sales of any of the common shares by the Selling Shareholders and any other such person. To the extent applicable, Regulation M may also restrict the ability of any person engaged in the distribution of the common shares to engage in market-making activities with respect to the common shares.

Underwriters or agents could make sales in privately negotiated transactions and/or any other method permitted by law, including sales deemed to be an at-the-market offering as defined in Rule 415 promulgated under the Securities Act, which includes sales made directly on or through Nasdaq, the existing trading market for our common shares, or sales made to or through a market maker other than on an exchange.

We will bear costs relating to all of the securities offered and sold by us under this registration statement.

EXPENSES

The following are the estimated expenses of the issuance and distribution of the securities being registered under the registration statement of which this prospectus forms a part, all of which will be paid by us.

LEGAL MATTERS

The validity of the securities offered by this prospectus and certain other legal matters relating to United States and Marshall Islands law are being passed upon for us by Watson Farley & Williams LLP, New York, New York.

EXPERTS

The financial statements of Rubico Inc. as of December 31, 2024 and 2025, and for each of the three years in the period ended December 31, 2025, incorporated in this registration statement by reference to Rubico’s annual report on Form 20-F for the year ended December 31, 2025, have been audited by Deloitte Certified Public Accountants S.A., an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm given their authority as experts in accounting and auditing.

The office of Deloitte Certified Public Accountants, S.A. is located at Fragoklissias 3a & Granikou Street, Maroussi, Athens 151 25, Greece.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form F-3 under the Securities Act, including relevant exhibits and schedules, under the Securities Act with respect to the securities offered by this prospectus. For the purposes of this section, the term registration statement on Form F-3 means the original registration statement on Form F-3 and any and all amendments including the schedules and exhibits to the original registration statement or any amendment. This prospectus, which constitutes a part of the registration statement, does not contain all of the information contained in the registration statement. Each statement made in this prospectus concerning a document filed as an exhibit to the registration statement on Form F-3 is qualified by reference to that exhibit for a complete statement of its provisions. You should read the registration statement on Form F-3 and its exhibits and schedules for further information with respect to us and the securities offered hereby.

We are required to file reports, including annual reports on Form 20-F, and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information regarding registrants that file electronically with the SEC. The address of the website is http://www.sec.gov. Additionally, we will make these filings available, free of charge, on our website at www.rubicoinc.com as soon as reasonably practicable after we electronically file such materials with, or furnish them to, the SEC. The information on our website, other than these filings, is not, and should not be, considered part of this prospectus and is not incorporated by reference into this document.

As a foreign private issuer, we will be exempt from the rules of the Exchange Act prescribing the furnishing and content of proxy statements to shareholders. Our executive officers, directors and principal shareholders are exempt from the short-swing profit recovery provisions contained in Section 16 of the Exchange Act. In addition, we will not be required under the Exchange Act to file periodic reports and financial statements with the SEC as frequently or as promptly as U.S. companies whose securities are registered under the Exchange Act.

Information Provided by the Company

We will furnish holders of our common shares with annual reports containing audited financial statements and a report by our independent registered public accounting firm. The audited financial statements will be prepared in accordance with U.S. GAAP. As a “foreign private issuer,” we are exempt from the rules under the Exchange Act prescribing the furnishing and content of proxy statements to shareholders. While we furnish proxy statements to shareholders in accordance with the rules of Nasdaq, those proxy statements do not conform to Schedule 14A of the proxy rules promulgated under the Exchange Act. In addition, as a “foreign private issuer,” our officers and directors are exempt from the rules under the Exchange Act relating to short swing profit reporting and liability.

DOCUMENTS INCORPORATED BY REFERENCE

The SEC allows us to “incorporate by reference” information that we file with it into this prospectus. This means that we can disclose important information to you by referring you to those filed documents. The information incorporated by reference is considered to be a part of this prospectus, and information that we file later with the SEC prior to the termination of this offering will also be considered to be part of this prospectus and will automatically update and supersede previously filed information, including information contained in this document. Any statement contained in this prospectus or a previously filed document incorporated by reference will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or a subsequently filed document incorporated by reference modifies or replaces that statement.

This prospectus incorporates by reference the following documents:

We are also incorporating by reference any documents that we file with the SEC after the date of the filing of the registration statement of which the prospectus forms a part and prior to the subsequent effectiveness of that registration statement, and all subsequent annual reports on Form 20-F that we file with the SEC and certain current reports on Form 6-K that we file with or furnish to the SEC pursuant to Section 13(a), 13(c) or 15(d) of the Exchange Act subsequent to the date of this prospectus until we file a post-effective amendment indicating that the offering of the securities made by this prospectus has been terminated.

You should rely only on the information contained or incorporated by reference in this prospectus and any accompanying prospectus supplement. We have not and the Selling Shareholders have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not and the Selling Shareholders are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and any accompanying prospectus supplement as well as the information we previously filed with the SEC and incorporated by reference, is accurate as of the dates on the front cover of those documents only. Our business, financial condition and results of operations and prospects may have changed since those dates.

We will provide without charge to each person, including any beneficial owner, to whom this prospectus is delivered, upon his or her written or oral request, a copy of any or all documents referred to above which have been or may be incorporated by reference into this prospectus. You may obtain a copy of these documents by writing to or telephoning us at the following address:

Rubico Inc.

20 Iouliou

Kaisara Str,

19002 Paiania,

Athens, Greece

+ 30 210 812 8107 (telephone number)

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

The Amended and Restated Bylaws of the Company provide that any person who is or was a director or officer of the Registrant, or is or was serving at the request of the Registrant as a director or officer of another partnership, joint venture, trust or other enterprise shall be entitled to be indemnified by the Company upon the same terms, under the same conditions, and to the same extent as authorized by Section 60 of the Business Corporation Act of the Republic of The Marshall Islands, if he acted in good faith and in a manner he reasonably believed to be in or not opposed to the best interests of the Registrant, and, with respect to any criminal action or proceeding, had reasonable cause to believe his conduct was unlawful.

There is currently no pending material litigation or proceeding involving any of our directors, officers or employees for which indemnification is sought.

Section 60 of the BCA provides as follows:

The exhibits filed as part of this registration statement are listed in the index to exhibits immediately preceding such exhibits, which index to exhibits is incorporated herein by reference.

The financial statements filed as part of this registration statement are listed in the index to the financial statements immediately preceding such financial statements, which index to the financial statements is incorporated herein by reference.

The undersigned registrant hereby undertakes:

Exhibit Index

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form F-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Athens, Country of Greece on July 1, 2026.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints each of Kalliopi Ornithopoulou and Will Vogel, with full power to act alone, his or her true and lawful attorney-in-fact and agent, with full powers of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including pre-effective or post-effective amendments) to this registration statement and any and all additional registration statements pursuant to Rule 462(b) of the Securities Act of 1933, as amended, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents full power and authority to do and perform each and every act and thing requisite and necessary to be done, as fully for all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or either of them or their or his or her substitute or substitutes, may lawfully do or cause to be done by virtue thereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons on July 1, 2026, in the capacities indicated.

AUTHORIZED REPRESENTATIVE

Pursuant to the Securities Act of 1933, the undersigned, the duly authorized representative in the United States of Rubico Inc., has signed this registration statement in the City of Newark, State of Delaware on July 1, 2026.

ATTACHMENTS / EXHIBITS

EXHIBIT 4.7

EXHIBIT 4.8

EXHIBIT 5.1

EXHIBIT 8.1

EXHIBIT 23.2

EXHIBIT 107

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