Filed pursuant to Rule 424(b)(5)

Registration No. 333-297207

PROSPECTUS SUPPLEMENT

(To Prospectus dated July 14, 2026)

$15,000,000 Principal Amount of Senior Convertible Notes,

Common Share Purchase Warrants,

Pre-Funded Warrants,

Common Shares Underlying the Senior Convertible Notes, Common Share Purchase Warrants, and Pre-Funded Warrants,

and

Common Shares Issuable as Commitment Shares

Rubico Inc.

Pursuant to a securities purchase agreement dated October 16, 2026 (the “Purchase Agreement”), we are offering to an institutional investor (i) our Senior Convertible Notes (the “Notes”) in an aggregate initial principal amount of up to $15,000,000, (ii) common shares, par value $0.01 per share, issuable from time to time upon conversion of the Notes, (iii) common share purchase warrants (the “Warrants,” and with the Notes, the “Securities”) to purchase common shares with an aggregate initial cash exercise price of up to $15,000,000, (iv) common shares issuable from time to time upon exercise of the Warrants, (v) common shares issuable at each closing of a sale of Notes and Warrants pursuant to the Purchase Agreement (the “Commitment Shares”) and/or pre-funded warrants issuable in lieu of Commitment Shares pursuant to the Purchase Agreement (the “Pre-Funded Warrants”) and (vi) common shares issuable from time to time upon exercise of the Pre-Funded Warrants (the “Pre-Funded Warrant Shares”).

The Notes will be issued in two tranches subject to the conditions of the Purchase Agreement. At the initial closing of this offering (the “First Tranche Closing”), subject to the terms and conditions of the Purchase Agreement, we will issue one or more Notes in the aggregate principal amount of $9,444,444 (the “First Tranche Notes”) and Warrants to purchase common shares with an aggregate initial cash exercise price of $9,444,444 (the “First Tranche Warrants”). We will receive gross proceeds of $8,500,000 in the First Tranche Closing.

In addition, we may issue and sell in a second closing (the “Second Tranche Closing”) on a date selected by us in our sole discretion subject to the conditions set forth in the Purchase Agreement, an additional $5,555,556 in aggregate principal amount of the Notes (the “Second Tranche Notes”) and Warrants to purchase common shares with an aggregate initial cash exercise price of $5,555,556 (the “Second Tranche Warrants”). We will receive gross proceeds of $5,000,000 in the Second Tranche Closing.

In addition, pursuant to the Purchase Agreement, we have agreed to issue common shares to the investor in this offering at the First Tranche Closing and the Second Tranche Closing (the “First Tranche Commitment Shares” and the “Second Tranche Commitment Shares,” respectively, and collectively the “Commitment Shares”), in each case in a number equal to 5% of the face value of the principal amount of the Notes issued at each closing divided by the Fixed Conversion Price (as defined below) with respect to the relevant tranche.

We are also offering to the investor, if its receipt of Commitment Shares would otherwise result in the investor’s, together with its Attribution Parties (as defined in the Pre-Funded Warrants), beneficial ownership exceeding 9.99% of our outstanding common shares immediately following the relevant closing, it will receive Pre-Funded Warrants in lieu of Commitment Shares for the amount of Commitment Shares that would cause the investor’s beneficial ownership of our common shares to exceed 9.99%. Each Pre-funded Warrant will be exercisable for one common share. Subject to limited exceptions, a holder of Pre-Funded Warrants will not have the right to exercise any portion of its Pre-Funded Warrants if the holder, together with its Attribution Parties (as defined in the Pre-Funded Warrants), would beneficially own in excess of 9.99% of the number of common shares outstanding immediately after giving effect to such exercise. The Pre-funded Warrants will be immediately exercisable (subject to the beneficial ownership cap) and may be exercised at any time until all of the Pre-funded Warrants are exercised in full. See “Description of Securities We Are Offering” in this prospectus supplement for more information.

The Notes will constitute unsecured obligations of ours. The Notes will have an original issue discount of 10.0% and bear interest at a rate of 8.0% per annum if paid in cash and 10.0% per annum if paid by conversion into common shares. Unless earlier converted or redeemed, the Notes will mature 12 months after issuance (the “Maturity Date”). We may, at our sole discretion, extend the Maturity Date by an additional six months (such election, the “Extension Election” and such new maturity date the “Extended Maturity Date”), provided that, upon any such extension, the outstanding principal amount of the applicable Note will be increased by 5.0%.

Outstanding principal and accrued interest under the Notes will be convertible immediately upon issuance of the Notes, at the option of the holder, into common shares at either (i) a fixed conversion price equal to the lower of (a) the Nasdaq Official Closing Price of our common shares on the trading day immediately preceding the date of issuance of the relevant Note or (b) the average Nasdaq Official Closing Price of our common shares for the five trading days immediately preceding the date of issuance of the relevant Note (the “Fixed Conversion Price”), or (ii) an alternate conversion price (the “Alternate Conversion Price”) equal to the greater of (a) 85.0% of the lowest daily volume-weighted average price (“VWAP”) during the 10 trading days preceding the relevant conversion date and (b) a floor price of $0.10 (the “Floor Price”). The Fixed Conversion Price will at no time be lower than the Floor Price. The Fixed Conversion Price, but not the Floor Price, will be adjusted for share dividends, share splits, stock combinations and other similar transactions. The Fixed Conversion Price upon issuance of the First Tranche Notes will be $0.3646.

The Warrants are exercisable immediately upon issuance and expire five years from the initial date of issuance. The exercise price of the Warrants shall be equal to the Fixed Conversion Price of the Notes issued on the same closing date as the relevant Warrants, subject to adjustment pursuant to the terms of the Warrants. Holders may, if a registration statement registering the issuance of the common shares underlying the Warrants under the Securities Act of 1933, as amended (the “Securities Act”) is not effective or available, exercise their Warrants, in whole or in part, by means of a “cashless exercise” in which the holder shall be entitled to receive a number of common shares as determined in accordance with the formula set forth therein. The First Tranche Warrants will have a per-share exercise price of $0.3646, subject to adjustment as set forth in the Warrants.

There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

For a more detailed description of the Notes and the Warrants, please see the sections of this prospectus supplement entitled “Description of Securities We Are Offering—Senior Convertible Notes” and “Description of Securities We Are Offering—Warrants.”

The common shares sold in this offering include preferred stock purchase rights which trade with the common shares and this prospectus supplement relates also to the offering of such preferred stock purchase rights.

There is no established public trading market for the Notes, Warrants or Pre-Funded Warrants, and we do not expect such markets to develop. We do not intend to apply to list the Notes, Warrants or Pre-Funded Warrants on any securities exchange.

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

We are a “foreign private issuer” and an “emerging growth company” under the U.S. federal securities laws as that term is used in the Jumpstart Our Business Startups Act of 2012 (the “JOBS Act”) and, as a result, have elected to comply with certain reduced public company disclosure and reporting requirements. In addition, as long as we remain an emerging growth company, we will qualify for certain limited exceptions from the Sarbanes-Oxley Act of 2002. See “Prospectus Summary—Implications of Being an Emerging Growth Company and a Foreign Private Issuer.”

We have retained Maxim Group LLC to act as the exclusive placement agent to use its best efforts to solicit offers from investors to purchase the securities in this offering. The placement agent has no obligation to buy any securities from us or to arrange for the purchase or sale of any specific number or dollar amount of securities. The placement agent is not purchasing or selling any securities in this offering. We will pay the placement agent a fee equal to 6.0% of the aggregate purchase price paid by investors in this offering.

We estimate the total expenses of this offering, excluding the placement agent fees, will be approximately $0.3 million. We are not required to sell the full number or dollar amount of the securities offered in this offering. After deducting fees due to the placement agent and our estimated offering expenses, we expect the net proceeds to us from this offering will be approximately $12.4 million, not including the exercise price of any Warrants or Pre-Funded Warrants.

We expect to deliver the First Tranche Notes, First Tranche Warrants and the related Commitment Shares and/or Pre-Funded Warrants in the First Tranche Closing to the purchaser on or about October 19, 2026, subject to the satisfaction of customary closing conditions.

Investing in our securities involves a high degree of risk and uncertainty. See “Risk Factors” beginning on page S-8 of this prospectus supplement, and in the accompanying prospectus and the documents we have filed with the Securities and Exchange Commission (the “SEC” or the “Commission”), that are incorporated by reference herein for more information, before you make any investment in our common shares.

None of the Commission, any state securities commission, or any other regulatory body has approved or disapproved of these securities or passed on the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

Maxim Group LLC

The date of this prospectus supplement is October 16, 2026

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

PROSPECTUS

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus. We have not authorized anyone else to provide you with additional or different information. We are offering to sell, and seeking offers to buy, securities only in jurisdictions where offers and sales are permitted. You should not assume that the information in this prospectus supplement or the accompanying prospectus is accurate as of any date other than the date on the front of those documents or that any document incorporated by reference is accurate as of any date other than its filing date.

No action is being taken in any jurisdiction outside the United States to permit a public offering of securities of the Company or possession or distribution of this prospectus supplement or the accompanying prospectus in that jurisdiction. Persons who come into possession of this prospectus supplement or the accompanying prospectus in jurisdictions outside the United States are required to inform themselves about and to observe any restrictions as to this offering and the distribution of this prospectus supplement and the accompanying prospectus applicable to that jurisdiction.

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the Commission, utilizing a “shelf” registration process.

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering described herein and the securities offered hereby, and also adds to and updates information contained in the accompanying base prospectus and the documents incorporated by reference into this prospectus supplement and the base prospectus.

The second part, the base prospectus, gives more general information about securities we may offer from time to time, some of which does not apply to this offering. Generally, when we refer only to the prospectus, we are referring to both parts combined, and when we refer to the accompanying prospectus, we are referring to the base prospectus.

If the description of this offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information contained in this prospectus supplement. This prospectus supplement, the accompanying base prospectus, any free writing prospectus and the documents incorporated into each by reference include important information about us, our securities being offered and other information you should know before investing. You should read this prospectus supplement and the accompanying base prospectus together with the additional information described under the heading “Where You Can Find More Information” before investing in our securities.

Any statement made in this prospectus supplement or in a document incorporated or deemed to be incorporated by reference into this prospectus supplement will be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or in any other subsequently-filed document that is also incorporated by reference into this prospectus supplement modifies or supersedes that statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

We have authorized only the information contained or incorporated by reference in this prospectus supplement, the accompanying prospectus, and any free writing prospectus prepared by or on behalf of us or to which we have referred you. We have not, and the placement agent has not, authorized anyone to provide you with information that is different. We and the placement agent take no responsibility for, and can provide no assurance as to the reliability of, any information that others may give you. If anyone provides you with different or inconsistent information, you should not rely on it. We are offering to sell our securities only in jurisdictions where offers and sales are permitted. The information contained in or incorporated by reference in the prospectus is accurate only as of the date such information was issued, regardless of the time of delivery of the prospectus or the date of any sale of our common shares.

Unless otherwise indicated, all references to “dollars” and “$” in this prospectus supplement are to, and amounts presented in, United States dollars and financial information presented in this prospectus supplement that is derived from financial statements incorporated by reference is prepared in accordance with accounting principles generally accepted in the United States.

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 supplement 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 (the “Annual Report”). 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.

PROSPECTUS SUPPLEMENT SUMMARY

This section summarizes certain of the information that is contained in this prospectus supplement 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 supplement 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. As an investor or prospective investor, you should review carefully the more detailed information that appears later in this prospectus supplement and the information incorporated by reference in this prospectus supplement, 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 supplement.

Unless otherwise indicated, references in this prospectus supplement 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 prospectus supplement to the “Former Parent” refer to Top Ships Inc.

Unless otherwise indicated, references to “U.S. dollars,” “dollars,” “USD” and “$” in this prospectus supplement 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, the one-for-twenty-five reverse stock split of our issued and outstanding common shares that became effective on June 26, 2026 and the common share dividend of 0.5 common shares for each outstanding common share payable on October 5, 2026.

Capitalized terms used but not defined in this prospectus shall have the meanings ascribed to them in our Annual Report.

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 5.6 years and the M/T Eco West Coast with an age of 5.4 years, each focusing on the transportation of crude oil.

We also have four newbuilding contracts, three for 47,499 dwt chemical/product oil carriers, scheduled for delivery in the second, third and fourth quarters of 2029, respectively, and one for the M/Y Sanlorenzo 1150Exp, a 60-meters megayacht, scheduled for delivery in the second quarter of 2027, which we intend to divest with the objective of releasing capital for redeployment towards our core tanker business.

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. and Roman Empire Inc. 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.

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, 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.

Implications of Being an Emerging Growth Company and 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.”

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 date we first sold our common shares pursuant to an effective registration statement under the Securities Act 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.

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.

THE OFFERING

RISK FACTORS

An investment in our common shares involves a high degree of risk and uncertainty. We have identified a number of risk factors which you should consider before investing in our common shares. You should consider carefully the risks set forth below, those risk factors set forth under the heading “Risk Factors” in our Annual Report and incorporated by reference in this prospectus supplement, as well as any amendment or update to our risk factors reflected in subsequent filings with the SEC, and in any other documents we have incorporated by reference in this prospectus supplement, as well as those under the heading “Risk Factors” in the accompanying prospectus before investing in our common shares. The occurrence of one or more of these risk factors could adversely affect our results of operations or financial condition.

Risks Related to this Offering

Since we have broad discretion in how we use the proceeds from this offering, we may use the proceeds in ways with which you disagree.

Our management will have significant flexibility in applying the net proceeds of this offering. You will be relying on the judgment of our management with regard to the use of these net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. It is possible that the net proceeds will be invested in a way that does not yield a favorable, or any, return for us. The failure of our management to use such funds effectively could have a material adverse effect on our business, prospects, financial condition, operating results and cash flow.

A large number of shares may be sold in the market following this offering, which may significantly depress the market price of our common shares.

The common shares underlying the Notes and Warrants sold in the offering, and the Commitment Shares will be freely tradable without restriction or further registration under the Securities Act. As a result, a substantial number of our common shares may be sold in the public market following this offering. If there are significantly more common shares offered for sale than buyers are willing to purchase, then the market price of our common shares may decline to a market price at which buyers are willing to purchase the offered common shares and sellers remain willing to sell our common shares.

There is no public market for our Notes, Warrants or Pre-Funded Warrants sold in this offering.

There is no established public trading market for the Notes, Warrants or Pre-Funded Warrants being offered in this offering, and we do not expect such markets to develop. In addition, we do not intend to apply to list the Notes, Warrants or Pre-Funded Warrants on any securities exchange. Without an active market, the liquidity of the Notes, Warrants or Pre-Funded Warrants will be limited.

The sale or availability for sale of common shares issuable upon conversion of the Notes and exercise of the Warrants may depress the price of our common shares and encourage short sales by third parties, which could further depress the price of our common shares.

To the extent that one or more investors in the Notes sell our common shares issued upon conversion of the Notes or exercise of the Warrants, the market price of such common shares may decrease due to the additional selling pressure in the market. In addition, the risk of dilution from issuances of such common shares may cause shareholders to sell their common shares, which could further contribute to any decline in the price of our common shares. Any downward pressure on the price of our common shares caused by the sale or potential sale of such common shares could encourage short sales by third parties. Such sales could place downward pressure on the price of our common shares by increasing the number of common shares being sold, which could further contribute to any decline in the market price of our common shares.

We may fail to meet the continued listing requirements of Nasdaq, which could cause our common shares to be delisted.

There can be no assurance that we will remain in compliance with Nasdaq’s listing qualification rules, or that our common shares will not be delisted, which could have an adverse effect on the market price of, and the efficiency of the trading market for, our common shares.

Our common shares may be delisted from Nasdaq if we do not satisfy applicable market value requirements.

In July 2026, the SEC approved a Nasdaq rule requiring companies listed on the Nasdaq Capital Market to maintain a market value of listed securities (“MVLS”) of at least $5,000,000 (the “MVLS Rule”). If a company’s MVLS remains below $5,000,000 for 30 consecutive business days, Nasdaq will issue a staff delisting determination, immediately suspend trading of the company’s securities and commence delisting proceedings, without a cure period. The approval of the MVLS Rule has been stayed pending action by the Commission, and the MVLS Rule is not currently in effect. As of October 16, 2026, the market value of our listed securities was less than $5,000,000. If the stay is lifted and our MVLS remains below $5,000,000 for 30 consecutive business days, our common shares would be suspended from trading on Nasdaq and subject to delisting. Delisting could reduce the liquidity and market price of our common shares, limit investors’ ability to trade our securities, and adversely affect our ability to raise capital or use our equity securities in strategic transactions.

We may not have sufficient funds to satisfy our obligations under the Notes when due, and our ability to make payments may be limited by restrictions in our current and future indebtedness.

Our ability to pay principal, interest and any other amounts due on the Notes will depend on our liquidity position and our operating and financial performance, which are subject to significant volatility in the shipping industry. Our business may not continue to generate cash flow from operations in the future sufficient to satisfy our obligations under the Notes. If we are unable to generate such cash flow, we may be required to adopt one or more alternatives, such as reducing or delaying investments or capital expenditures, selling assets, refinancing or obtaining additional equity capital on terms that may be onerous or highly dilutive. Our ability to refinance the Notes may therefore depend on market conditions in our industry and in the capital markets and on our financial condition at such time. Therefore, we may not be able to engage in any of these activities or engage in these activities on desirable terms, which could result in a default on the Notes.

In addition, our financing arrangements in the form of the bareboat charters in connection with the SLBs of our vessels contain, and any future financing arrangements we may enter into are expected to contain, customary covenants, event of default and termination event clauses, including cross-default provisions and restrictive covenants and performance requirements that may affect our operational and financial flexibility. Such restrictions could affect, and in many respects limit or prohibit, among other things, our ability to incur additional indebtedness, pay dividends, create liens, sell assets or engage in mergers or acquisitions. These restrictions could also limit our ability to plan for or react to market conditions or meet extraordinary capital needs or otherwise restrict corporate activities. There can be no assurance that such restrictions will not adversely affect our ability to finance our future operations or capital needs, and may increase the risk that we will be unable to meet our obligations under the Notes when due.

The Notes will be unsecured obligations and will be effectively subordinated to our secured indebtedness, which could limit your ability to recover your investment.

The Notes will be our unsecured obligations and will not be guaranteed by any of our subsidiaries. Although the Notes are contractually senior in right of payment to all of our other liabilities other than indebtedness secured by liens on our vessels, the Notes will be effectively subordinated to our existing and future indebtedness secured by liens on our vessels (including, without limitation, indebtedness secured by mortgages on our vessels and related collateral, and our obligations under sale and leaseback financing arrangements in respect of our vessels) to the extent of the value of the collateral securing that indebtedness. In a bankruptcy, liquidation, dissolution, reorganization or similar proceeding, our assets and the assets of our subsidiaries would be available to satisfy the claims of such secured creditors before any payment could be made on the Notes. As a result, you may receive significantly less than the principal amount of your Notes upon any such event, or you may receive nothing at all.

The holders of the Notes will not have the rights or privileges of a holder of our common shares, including any voting rights, until such holder converts their Notes and acquires our common shares.

The holders of the Notes will not have the rights or privileges of a holder of our common shares, including any voting rights, until such holder converts their Notes and acquires our common shares. As a result, absent conversion of the Note, a holder of the Note will not have the ability to vote their common shares underlying the Note, which may limit the influence that the investor in our offering may have over the outcome of matters submitted to our shareholders for a vote.

You may be subject to tax if we make or fail to make certain adjustments to the applicable conversion rate of the Note even though you do not receive a corresponding cash distribution.

The conversion rate is subject to adjustment in certain circumstances, including the payment of cash dividends. If the applicable conversion rate is adjusted as a result of a distribution that is taxable to our common shareholders, such as a cash dividend, you may be deemed to have received a dividend subject to U.S. federal income tax without the receipt of any cash. In addition, a failure to adjust (or to adjust adequately) the applicable conversion rate after an event that increases your proportionate interest in us could be treated as a deemed taxable dividend to you.

As a newly incorporated company, we may not have the surplus or net profits required by law to pay dividends. The declaration and payment of dividends will always be subject to the discretion of our Board of Directors and will depend on a number of factors. Our Board of Directors may not declare dividends in the future.

The declaration, timing and amount of any dividend are subject to the discretion of our Board of Directors and will be dependent upon our earnings, financial condition, market prospects and our growth strategy, capital expenditure requirements, dividends to holders of our preferred shares, investment opportunities, restrictions in our financing arrangements, the provisions of Marshall Islands law affecting the payment of dividends to shareholders, overall market conditions and other factors.

In addition, we may incur expenses or liabilities, including extraordinary expenses, decreases in revenues, including as a result of unanticipated off-hire days or loss of a vessel, or increased cash needs, or be subject to other circumstances in the future, including as a result of the risks described in our Annual Report and any future reports we may file with the SEC, that could reduce or eliminate the amount of cash that we have available for distribution as dividends. Our growth strategy contemplates that we will finance the acquisition of additional vessels in part through raising equity capital. However, if external sources of funds on terms acceptable to us are limited, our Board of Directors may determine to finance acquisitions with cash from operations, which would reduce or even eliminate the amount of cash available for the payment of dividends. In addition, any credit facilities that we may enter into or the terms of preferred shares which we may issue in the future may include restrictions on our ability to pay dividends on our common shares. Further, under the terms of our current financing arrangements, and possibly any future financing arrangements, we will not be permitted to pay dividends that would result in an event of default or a termination event or if an event of default or a termination event has occurred and is continuing. As a result of these and other factors, we cannot assure you that our Board of Directors will declare dividend payments on our common shares in the future.

Further, Marshall Islands law generally prohibits the payment of dividends if the company is insolvent or would be rendered insolvent upon payment of such dividend, and dividends may be declared and paid out of our operating surplus. Dividends may also be declared or paid out of net profits for the fiscal year in which the dividend is declared and for the preceding fiscal year. As a newly incorporated company, we may not have the required surplus or net profits to pay dividends, and we may be unable to pay dividends in any anticipated amount or at all.

We have experienced and may in the future experience rapid and substantial share price volatility unrelated to our actual or expected operating performance, financial condition or prospects, making it difficult for prospective investors to assess the rapidly changing value of our common shares.

As a relatively small-capitalization company with relatively small public float, we may experience greater share price volatility, extreme price run-ups or rapid price declines, larger spreads in bid and ask prices, lower trading volume and less liquidity than large-capitalization companies. Such volatility, including any share price run-up, may be unrelated to our actual or expected operating performance, financial condition or prospects, making it difficult for prospective investors to assess the rapidly changing value of our common shares. In addition, holders of our common shares may experience losses, which may be material, if the price of our common shares declines after this offering or if such investors purchase our common shares prior to any price decline.

For example, on July 16, 2026, the trading price of our common shares ranged from an intra-day high of $4.46 to an intra-day low of $2.03 on trading volume of approximately 39.1 million shares.

Furthermore, if the trading volumes of our common shares are low, investors buying or selling in relatively small quantities may be able to easily influence the price of our common shares. Such low volume of trades could also cause the price of our common shares to fluctuate greatly, with large percentage changes in share price occurring in any trading day session. Holders of our common shares may also not be able to readily liquidate their investment or may be forced to sell at depressed prices due to low volume trading. Broad market fluctuations and general economic and political conditions may also adversely affect the market price of our common shares. As a result of this volatility, investors may experience losses on their investment in our common shares. A decline in the market price of our common shares also could adversely affect our ability to issue additional common shares or other securities and our ability to obtain additional financing in the future.

USE OF PROCEEDS

We estimate that the net proceeds from the sale of the securities offered by this prospectus supplement and sold in the First Tranche Closing and Second Tranche Closing, after deducting the placement agent fees and other estimated expenses of this offering payable by us, but not giving effect to any cash exercise of Warrants or Pre-Funded Warrants, will be approximately $12.4 million.

The net proceeds of this offering will be used for general corporate purposes, which may include, among other things, funding for working capital needs, debt repayments, construction of our newbuilding vessels, the payment of the outstanding balance of the purchase price payable to our Former Parent for the acquisition of Roman Shark V Inc. and the acquisition of additional secondhand or newbuilding vessels in accordance with our business strategy. However, we have not identified any potential acquisitions, and we can provide no assurance that we will be able to complete the acquisition of any additional vessels that we are able to identify.

CAPITALIZATION

The following table sets forth our capitalization and indebtedness as of June 30, 2026: 

Based on our unaudited interim condensed consolidated financial statements of Rubico Inc. as of June 30, 2026:

Expressed in thousands of U.S. dollars

DESCRIPTION OF CAPITAL STOCK

You should carefully review the description of our share capital under the heading “Item 10. Additional Information” in our Annual Report incorporated by reference herein.

DESCRIPTION OF SECURITIES WE ARE OFFERING

Senior Convertible Notes

The material terms and provisions of the Notes being registered pursuant to this prospectus supplement are summarized below. The form of the Notes will be filed with the SEC as an exhibit to a Form 6-K in connection with this offering. The following summary of certain material terms of the Notes is qualified in its entirety by reference to the form of Notes.

Maturity Date

Unless earlier converted, redeemed or accelerated upon an Event of Default, the Notes mature twelve months from their date of issuance. On the Maturity Date, the Company is required to pay in cash the remaining unconverted principal amount of the Notes multiplied by 1.05 (or 1.18 if an Event of Default has occurred and is continuing), plus accrued and unpaid interest.

The Company may elect, in its sole discretion, to extend the maturity date (the “Maturity Date”) once for an additional six-month period by providing written notice to the holder at least five business days prior to the Maturity Date. Upon any such extension, the outstanding principal amount of the applicable Note as of the date of such notice will be increased by 5.0%.

Interest

The Notes accrue interest at a rate of 8.0% per annum if paid in cash and 10.0% per annum if paid in common shares. Interest is payable in cash at maturity and upon mandatory or optional redemption. Upon conversion of the Notes accrued interest with respect to the principal amount being converted is payable through conversion into common shares.

While an Event of Default under the Notes has occurred and is continuing, the Notes will accrue interest at a rate equal to the lesser of 18.0% per annum or the maximum rate permitted under applicable law.

Any overdue accrued and unpaid interest accrues a late fee following the Maturity Date or Extended Maturity Date, as applicable, at a rate equal to the lesser of 12.0% per annum or the maximum rate permitted by applicable law.

Ranking

The Notes constitute senior unsecured obligations of the Company. The Notes rank pari passu with the other notes issued pursuant to the Purchase Agreement and, pursuant to their terms, are contractually senior in right of payment to all other liabilities of the Company and its subsidiaries, other than indebtedness secured by liens on vessels.

Conversion at the Option of the Holder; Conversion Price; Alternate Conversion Price

At the option of the holder all or any portion of a Note may be converted, together with accrued and unpaid interest thereon, into common shares at any time while the Note remains outstanding.

The number of common shares issuable upon conversion is determined by the quotient obtained by dividing the outstanding principal amount of the Notes to be converted plus all accrued and unpaid interest thereon attributable to such principal amount, by the Fixed Conversion Price or, if the holder elects an alternate conversion, the Alternate Conversion Price. Neither the Fixed Conversion Price nor the Alternate Conversion Price will at any time be lower than the Floor Price.

The Company is required to deliver conversion shares by the earlier of one trading day or the standard settlement period following each conversion date, and is subject to buy-in and rescission remedies if it fails to do so. The Company is also required to reserve out of its authorized and unissued common shares not less than 200% of the number of common shares issuable upon conversion of the outstanding Notes at the Alternate Conversion Price then in effect and, if it does not have sufficient authorized shares to do so, to hold a meeting of its shareholders within 60 days to approve an increase in its authorized common shares.

Beneficial Ownership Limitation

A holder may not convert any portion of a Note to the extent that, after giving effect to such conversion, the holder together with its Attribution Parties (as defined in the Note) would beneficially own more than 9.99% of the Company's outstanding common shares. The holder may decrease such percentage, or increase it to any percentage not in excess of 9.99%, upon written notice to the Company, provided that any increase will not be effective until the 61st day after such notice is delivered.

Holder Redemption Rights

Future Financing Redemption

If the Company raises capital in any equity or equity-linked financing, other than a Related Party Financing Transaction (as defined in the Purchase Agreement), the holder may require the Company to use 30% of the aggregate net proceeds of such financing to redeem all or a portion of the Notes outstanding. Any such redemption will be effected in cash at a price equal to 110% of the principal amount being redeemed, plus accrued and unpaid interest thereon (the “Redemption Price”).

Change of Control Redemption

Upon the occurrence of a Change of Control Transaction, as defined within the Note, the holder may require the Company to redeem all or a portion of the outstanding Notes for cash at the Redemption Price.

Optional Redemption by the Company

The Company may redeem all or any portion of the outstanding Notes at any time upon at least 35 days' prior written notice to the holder. Any such redemption must be made at the Redemption Price. During the notice period, the holder retains the right to convert the Notes.

Events of Default

The Notes contain customary events of default, including, among others: failure to pay principal, interest or other amounts when due (subject to a three trading day cure period for interest and other amounts); failure to observe or perform any other covenant or agreement in the Notes or any other transaction document that is not cured within the earlier of five trading days after notice and ten trading days after the Company becomes or should have become aware of such failure; a default or event of default under any transaction document or any other material agreement, lease, document or instrument to which the Company or any subsidiary is obligated, subject to a ten trading day cure period; material misrepresentations, subject to a ten trading day cure period where curable; bankruptcy events; a default under other indebtedness involving an obligation greater than $500,000 that results in such indebtedness being declared due and payable prior to its maturity; the common shares not being eligible for listing or quotation on a trading market and not being eligible to resume listing or quotation within five trading days; the Company being party to a Change of Control Transaction or Fundamental Transaction, or agreeing to sell or dispose of all or in excess of 50% of its assets (other than pursuant to a sale-leaseback or similar financing arrangement of vessels); any breach of an agreement delivered to the initial holders pursuant to Section 2.3 of the Purchase Agreement; a false or inaccurate certification as to the satisfaction of the Equity Conditions or as to whether an Event of Default has occurred; failure to deliver conversion shares or warrant shares prior to the fifth trading day after the applicable conversion date or exercise date, or notice of the Company’s intention not to honor conversion requests; the electronic transfer of the common shares through DTC no longer being available or being subject to a “chill”; unsatisfied judgments in excess of $500,000 for 45 days; the occurrence of a material adverse effect; and failure to obtain shareholder approval of an increase in authorized common shares within the required time period following an authorized share failure (each, an “Event of Default”). Upon an Event of Default, at the holder’s election, the Original Funded Principal (as defined in the Note), together with accrued interest and other amounts owing, becomes immediately due and payable in cash, and the Original OID Principal (as defined in the Note) becomes immediately due and payable in a number of common shares equal to such amount divided by the closing price of our common shares, with acceleration being automatic upon a bankruptcy event.

Adjustments

The Notes provide for customary adjustments in the event of stock dividends, stock splits, reverse stock splits, reclassifications and similar transactions. In addition, Note holders are entitled to participate in dividends, distributions and rights offerings as though the Notes had been fully converted immediately prior to the applicable record date (and, in the case of rights offerings, assuming conversion at the Alternate Conversion Price), provided that any participation that would cause the holder to exceed the beneficial ownership limitation will be held in abeyance until it would no longer do so.

Upon the occurrence of a Fundamental Transaction, as defined within the Note, the holder will be entitled to receive the same kind and amount of securities, cash or other property that the holder would have received if the Notes had been converted immediately prior to such transaction.

Covenants

The Notes contain customary affirmative and negative covenants. Among other things, the Company and its subsidiaries are restricted, subject to customary exceptions and permitted baskets, from:

In addition, if the closing price of our common shares is less than $0.50 for five consecutive trading days, we are required to take all actions, including seeking any required shareholder approvals and amending our charter documents, to effect a reverse share split with a ratio of at least 1-for-5 that is effective within 30 trading days.

Transferability

The Notes may be transferred or exchanged only in compliance with the Purchase Agreement and applicable securities laws.

Exchange Listing

The Company does not intend to list the Notes on any securities exchange or trading market. As a result, an active trading market for the Notes is not expected to develop.

Governing Law

The Notes are governed by the laws of the State of New York.

Warrants and Pre-Funded Warrants

The material terms and provisions of the Warrants and Pre-Funded Warrants are summarized below. The form of the Warrant and form of the Pre-Funded Warrant will be filed as an exhibit to a Form 6-K with the SEC in connection with this offering. The following summaries of certain material terms of the Warrants and Pre-Funded Warrants are qualified in their entirety by reference to the form of Warrant and form of Pre-Funded Warrant.

General

The number of common shares issuable upon exercise of the Warrants will equal 100% of the aggregate principal amount of the Notes issued in the relevant tranche, divided by the applicable Fixed Conversion Price under the Notes. If the investor’s receipt of Commitment Shares would otherwise result in the investor’s, together with its Attribution Parties (as defined in the Pre-Funded Warrants), beneficial ownership of our common shares exceeding 9.99% of our outstanding common shares immediately following the relevant closing, it will receive Pre-Funded Warrants in lieu of Commitment Shares for the amount of Commitment Shares that would cause the investor’s beneficial ownership of our common shares to exceed 9.99%.

Exercisability

The Warrants are exercisable immediately upon issuance and expire five years from the initial date of issuance The Pre-Funded Warrants are exercisable immediately upon issuance and remain exercisable until they are exercised in full.

The Warrants and Pre-Funded Warrants will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice with payment in full in immediately available funds for the number of common shares purchased upon such exercise (except in the case of a cashless exercise, as discussed below).

We may be required to pay certain amounts as liquidated damages as specified in the Warrants and Pre-Funded Warrants in the event we do not deliver common shares upon exercise of the Warrants and Pre-Funded Warrants within the time periods specified in the Warrants and Pre-Funded Warrants.

No fractional common shares will be issued in connection with the exercise of a Warrant or Pre-Funded Warrants.

Cashless Exercise

If a registration statement registering the issuance of the common shares underlying the Warrants under the Securities Act is not effective or available, the holder may, in its sole discretion, elect to exercise the Warrant through a cashless exercise, in which case the holder would receive upon such exercise the net number of common shares determined according to the formula set forth in the Warrant.

The Pre-Funded Warrants may be exercised, in whole or in part, in the holder’s sole discretion through a cashless exercise at any time, in which case the holder would receive upon such exercise the net number of common shares determined according to the formula set forth in the Pre-Funded Warrants.

Exercise Limitation

A holder will not have the right to exercise any portion of the Warrants if the holder (together with its Attribution Parties (as defined in the Warrants)) would beneficially own in excess of 4.99% of the number of our common shares outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the Warrants. However, any holder may increase or decrease such percentage to any other percentage not in excess of 9.99%, upon at least 61 days’ prior notice from the holder to us with respect to any increase in such percentage.

A holder will not have the right to exercise any portion of the Pre-Funded Warrants if the holder (together with its Attribution Parties (as defined in the Pre-Funded Warrants) would beneficially own in excess of 9.99% of the number of our common shares outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the Pre-Funded Warrants. However, any holder may increase or decrease such percentage to any other percentage not in excess of 9.99%, upon at least 61 days’ prior notice from the holder to us with respect to any increase in such percentage.

Exercise Price

The exercise price under each Warrant will initially equal 100% of the Fixed Conversion Price of the Notes in the relevant tranche.

The exercise price and the number of common shares issuable upon exercise of the Warrants are subject to customary anti-dilution adjustments for stock dividends, stock splits, reverse stock splits, reclassifications and similar events.

If the Company grants purchase rights, rights offerings, dividends or other distributions to holders of common shares, the holder of the Warrants generally will be entitled to participate in such transactions on the same basis as if the Warrants had been exercised immediately prior to the applicable record date, subject to the beneficial ownership limitation.

Upon the occurrence of a Fundamental Transaction, as defined in the Warrant, the holder will be entitled, upon exercise of the Warrants, to receive the same type and amount of consideration that the holder would have received if the Warrants had been exercised immediately prior to the transaction.

The exercise price for the Pre-funded Warrants is $0.01 per common share.

If the Company grants purchase rights, rights offerings, dividends or other distributions to holders of common shares, the holder of the Pre-Funded Warrants generally will be entitled to participate in such transactions on the same basis as if the Pre-Funded Warrants had been exercised immediately prior to the applicable record date, subject to the beneficial ownership limitation.

Upon the occurrence of a Fundamental Transaction, as defined in the Pre-Funded Warrant, the holder will be entitled, upon exercise of the Pre-Funded Warrants, to receive the same type and amount of consideration that the holder would have received if the Pre-Funded Warrants had been exercised immediately prior to the transaction. 

Authorized Shares

For so long as the Warrants and the Pre-Funded Warrants remain outstanding, the Company is required to reserve from its authorized and unissued common shares a sufficient number of shares to permit the full exercise of the Warrants and Pre-Funded Warrants.

Transferability

Subject to applicable securities laws, the Warrants and Pre-Funded Warrants may be sold, assigned or otherwise transferred without the consent of the Company.

Exchange Listing

The Company does not intend to list the Warrants or Pre-Funded Warrants on any securities exchange or trading market. Accordingly, no active trading market for the Warrants or Pre-Funded Warrants is expected to develop.

Governing Law

The Warrants and Pre-Funded Warrants are governed by New York law in accordance with the Purchase Agreement.

No Cash Settlement

Except for specified liquidated damages and buy-in remedies, the Company is not required to settle the Warrants or Pre-Funded Warrants in cash.

Transfer Agent and Registrar

The transfer agent and registrar for our common shares is Broadridge Financial Solutions, Inc.

Listing

Our common shares are traded on Nasdaq under the symbol “RUBI.” 

PLAN OF DISTRIBUTION

Pursuant to a placement agency agreement, dated as of October 16, 2026, we have engaged Maxim Group LLC to act as our exclusive placement agent to solicit offers to purchase the securities offered by this prospectus supplement. The Placement Agent is not purchasing or selling any of our securities offered by this prospectus supplement, nor is it required to arrange the purchase or sale of any specific number or dollar amount of our securities, but has agreed to use its reasonable best efforts to arrange for the sale of all of our securities offered hereby. We have entered into a securities purchase agreement directly with the investor in connection with this offering and we may not sell the entire amount of securities offered pursuant to this prospectus supplement.

Placement Agent Fees, Commissions and Expenses

Upon the closing of this offering, we will pay the Placement Agent a cash transaction fee equal to 6.0% of the aggregate gross cash proceeds to us from the sale of the securities in the offering. In addition, we will reimburse the Placement Agent for its out-of-pocket expenses incurred in connection with this offering, including the fees and expenses of the counsel for the Placement Agent, up to $50,000.

We estimate that the total expenses of the offering, including registration, filing and listing fees, printing fees and legal and accounting expenses, but excluding Placement Agent fees, will be approximately $0.3 million, all of which are payable by us. This figure includes the Placement Agent’s accountable expenses, including, but not limited to, legal fees for Placement Agent’s legal counsel, that we have agreed to pay at the closing of the offering up to an aggregate expense reimbursement of $50,000.

Lock-Up Agreements

We have agreed for a period of thirty trading days from the applicable closing, not to issue, enter into any agreement to issue or announce the issuance or proposed issuance of any common shares or common share equivalents, subject to certain exceptions set forth in the securities purchase agreement. We have also agreed, subject to certain exceptions, to a restriction on the issuance of any variable priced securities until six months after the applicable closing hereunder.

Participation in Future Financing

We are obligated to, from the date of the Securities Purchase Agreement until the date that is three months after the first date on which the aggregate outstanding principal amount of the Notes is less than 5% of the aggregate principal amount of such Notes upon issuance, and upon any issuance by us or any of our subsidiaries of indebtedness, preferred shares, common shares, options or securities convertible into common shares, other than certain exempt issuances and specified vessel-related financing transactions, provide the purchasers with the right to participate in such offering on the same terms, conditions and price provided for in the offering. The purchasers may collectively participate in an amount of up to 50% of the total offering, with each purchaser entitled to purchase its pro rata portion of such amount based on its subscription amount relative to the aggregate subscription amounts of all participating purchasers.

Indemnification

We have agreed to indemnify the Placement Agent against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the Placement Agent may be required to make for these liabilities.

 Determination of Offering Price and Exercise Price

The actual public offering price of the securities we are offering was negotiated between us and the investor in the offering based on the trading of our common shares prior to the offering, among other things. Other factors considered in determining the public offering price of the securities we are offering include our history and prospects, the stage of development of our business, our business plans for the future and the extent to which they have been implemented, an assessment of our management, the general conditions of the securities markets at the time of the offering and such other factors as were deemed relevant.

 Regulation M

The Placement Agent may be deemed to be an underwriter within the meaning of Section 2(a)(11) of the Securities Act, and any commissions received by it and any profit realized on the resale of the securities sold by it while acting as principal might be deemed to be underwriting discounts or commissions under the Securities Act. As an underwriter, the Placement Agent would be required to comply with the requirements of the Securities Act and the Exchange Act, including, without limitation, Rule 10b-5 and Regulation M under the Exchange Act. These rules and regulations may limit the timing of purchases and sales of our securities by the Placement Agent acting as principal. Under these rules and regulations, the Placement Agent (i) may not engage in any stabilization activity in connection with our securities and (ii) may not bid for or purchase any of our securities or attempt to induce any person to purchase any of our securities, other than as permitted under the Exchange Act, until it has completed its participation in the distribution.

Electronic Distribution

A prospectus in electronic format may be made available on a website maintained by the Placement Agent. In connection with the offering, the Placement Agent or selected dealers may distribute prospectuses electronically. No forms of electronic prospectus other than prospectuses that are printable as Adobe® PDF will be used in connection with this offering.

Other than the prospectus in electronic format, the information on the Placement Agent’s website and any information contained in any other website maintained by the Placement Agent is not part of the prospectus or the registration statement of which this prospectus supplement forms a part, has not been approved and/or endorsed by us or the Placement Agent in its capacity as placement agent and should not be relied upon by investors.

Certain Relationships

The Placement Agent and its affiliates have and may in the future provide, from time to time, investment banking and financial advisory services to us in the ordinary course of business, for which they may receive customary fees and commissions. The Placement Agent acted as placement agent and warrant agent in connection with our public offering and warrant inducement transaction consummated in May 2026 and June 2026, respectively, for which it received compensation.

Listing

Our common shares are listed on Nasdaq under the symbol “RUBI”.

MATERIAL U.S. FEDERAL INCOME AND MARSHALL ISLANDS TAX CONSIDERATIONS OF THE SECURITIES

The following represents the opinion of our United States and Marshall Islands tax counsel, Watson Farley & Williams LLP, and is a summary of the material U.S. federal income tax and Marshall Islands tax consequences of the ownership and disposition of our Securities.

U.S. Federal Income Tax Considerations

This section is a discussion of the material U.S. federal income tax considerations to a U.S. holder (as defined below) relating to (i) the purchase, ownership, disposition and conversion of the Notes, (ii) the purchase, ownership, disposition, exercise and lapse of the Warrants, (iii) the purchase, ownership, disposition and exercise of the Pre-Funded Warrants, and (iv) the ownership and disposition of the Commitment Shares and the common shares into which the Notes may be converted or for which the Warrants and Pre-Funded Warrants may be exercised. The information provided below is based on existing U.S. federal income tax authorities, all of which are subject to change or differing interpretations, possibly with retroactive effect. We cannot give any assurances that the Internal Revenue Service (the “IRS”) will not challenge one or more of the tax consequences described herein, and we have not obtained, nor do we intend to obtain, a ruling from the IRS with respect to the U.S. federal income tax consequences of purchasing, owning, disposing of or converting the Notes, purchasing, owning, disposing of, exercising or the lapse of the Warrants, purchasing, owning, disposing of or exercising the Pre-Funded Warrants, or owning or disposing of the Commitment Shares or the common shares into which the Notes may be converted or for which the Warrants or Pre-Funded Warrants may be exercised. The summary generally applies only to U.S. holders of the Securities who acquire the Securities offered in this offering on original issuance, and that hold the Securities (or common shares into which the Notes may be converted or for which the Warrants or Pre-Funded Warrants may be exercised) as “capital assets” within the meaning of Section 1221 of the Internal Revenue Code of 1986, as amended (the “Code”) (generally, property held for investment). This discussion does not purport to deal with all aspects of U.S. federal income taxation that may be relevant to a particular beneficial owner in light of the beneficial owner’s circumstances (for example, persons subject to the alternative minimum tax provisions of the Code, or a U.S. holder (as defined below) whose “functional currency” is not the U.S. dollar). Also, this discussion is not intended to be wholly applicable to all categories of investors, some of which may be subject to special rules (such as partnerships and pass-through entities and investors in such entities, dealers in securities or currencies, traders in securities that elect to use a mark-to-market method of accounting, banks, thrifts, regulated investment companies, real estate investment trusts, insurance companies, tax-exempt entities, tax-deferred or other retirement accounts, certain former citizens or residents of the United States, persons holding the Securities or common shares as part of a hedging, conversion or integrated transaction or a straddle, persons that own, or are deemed to own, 10% or more (by vote or value) of our shares, persons deemed to sell the Securities or common shares under the constructive sale provisions of the Code, or persons required under Section 451(b) of the Code to conform the timing of income accruals with respect to the Securities or common shares to their financial statements). Finally, the summary does not address the effects of the U.S. federal estate and gift tax laws or any applicable non-U.S., state or local laws. 

AN INVESTOR CONSIDERING THE PURCHASE OF THE SECURITIES SHOULD CONSULT THE INVESTOR’S OWN TAX ADVISORS REGARDING THE APPLICATION OF THE U.S. FEDERAL INCOME TAX LAWS TO ANY PARTICULAR SITUATIONS AND THE CONSEQUENCES OF U.S. FEDERAL ESTATE AND GIFT TAX LAWS, NON-U.S., STATE AND LOCAL LAWS, AND TAX TREATIES.

As used herein, the term “U.S. holder” means a beneficial owner of the Securities or the common shares into which the Notes may be converted or for which the Warrants or Pre-Funded Warrants may be exercised that, for U.S. federal income tax purposes is (1) an individual who is a citizen or resident of the United States, (2) a corporation, or an entity treated as a corporation for U.S. federal income tax purposes, created or organized in or under the laws of the United States or any state of the United States, or the District of Columbia, (3) an estate the income of which is subject to U.S. federal income taxation regardless of its source, or (4) a trust if it (x) is subject to the primary supervision of a U.S. court and one or more U.S. persons have the authority to control all substantial decisions of the trust or (y) has a valid election in effect under applicable U.S. Treasury regulations to be treated as a U.S. person.

If a partnership (including an entity or arrangement, domestic or foreign, treated as a partnership for U.S. federal income tax purposes) is a beneficial owner of the Securities or common shares acquired upon conversion of the Notes or exercise of the Warrants or Pre-Funded Warrants, the tax treatment of a partner in the partnership will depend upon the status of the partner and the activities of the partnership. A beneficial owner of the Securities or common shares acquired upon conversion of the Notes or exercise of the Warrants or Pre-Funded Warrants that is a partnership, and partners in such partnership, should consult their own tax advisors about the U.S. federal income tax consequences of purchasing, owning, disposing of, or converting the Notes, purchasing, owning, disposing of, exercising or the lapse of the Warrants, purchasing, owning, disposing of or exercising the Pre-Funded Warrants and owning and disposing of the Commitment Shares or the common shares into which the Notes may be converted or for which the Warrants or Pre-Funded Warrants may be exercised.

Characterization of the Securities

We intend to treat the Securities as an “investment unit” for U.S. federal income tax purposes. The purchase price paid for the investment unit must be allocated between the Notes, Warrants, Pre-Funded Warrants and Commitment Shares, each based on their relative fair market values at the time of the sale, and the portion of such purchase price allocated to the Notes will be the issue price of the Notes. Our allocation of the purchase price between the Notes and the other Securities is binding on a U.S. holder of the investment unit, unless the U.S. holder explicitly discloses that the U.S. holder’s allocation is different from our allocation. The disclosure generally must be made on a statement attached to the U.S. holder’s timely filed U.S. federal income tax return for the taxable year that includes the U.S. holder’s purchase of the investment unit. We cannot give any assurance that the IRS will respect our allocation or, as applicable, a U.S. holder’s allocation. If the IRS successfully challenges our allocation or, as applicable, a U.S. holder’s allocation, the tax consequences resulting from the new allocation could be different from the tax consequences resulting from our allocation or, as applicable, the U.S. holder’s allocation. U.S. holders should consult their tax advisors regarding the tax treatment of the Securities and the allocation of the purchase price among the Notes, Warrants, Pre-Funded Warrants and Commitment Shares.

Taxation of Interest and Original Issue Discount

For U.S. federal income tax purposes, the Notes will have original issue discount (“OID”) if the excess of the stated redemption price at maturity over their issue price is greater than or equal to a de minimis amount (generally 1⁄4 of 1% of the stated redemption price at maturity multiplied by the number of complete years to maturity from the issue date). The issue price of the Notes will be determined based on an allocation of the purchase price between the Notes and the other Securities, as described in “—Characterization of the Securities” above. The stated redemption price at maturity of the Notes is the sum of all payments other than payments of “qualified stated interest.” “Qualified stated interest” includes stated interest that is unconditionally payable in cash or property (other than debt instruments of the issuer) at least annually at a single fixed rate (with certain exceptions for lower rates paid during some periods) or certain variable rates as described below. Interest is payable at a single fixed rate only if the rate appropriately takes into account the length of the interval between payments. For purposes of determining whether interest is payable at least annually, where the issuer has a unilateral option to extend the interest payment date, the issuer is deemed to exercise or not exercise the option in a manner that minimizes the yield on the debt instrument.

The amount of OID includible in taxable income of a U.S. holder is the sum of the daily portions of OID with respect to the Notes for each day during the taxable year on which the Notes are held. Generally, the daily portion of OID is determined by allocating to each day in any “accrual period” a ratable portion of the OID allocable to such accrual period. A U.S. holder may select the “accrual periods” for the Notes, which may be of any length, and may vary in length over the term of the Notes, provided that each accrual period is no longer than one year and each scheduled payment of principal or interest occurs either on the first day or final day of an accrual period. The amount of OID allocable to each accrual period is equal to the excess (if any) of (a) the product of the Notes’ adjusted issue price at the beginning of such accrual period and their yield to maturity (determined on a constant yield basis, compounded at the close of each accrual period and adjusted for the length of such accrual period), over (b) the amount of qualified stated interest, if any, payable on the Notes and allocable to such accrual period. The “adjusted issue price” of the Notes at the beginning of any accrual period generally is the issue price of the Notes increased by the accrued OID allocable for all prior accrual periods and reduced by any prior payment on the Notes other than a payment of qualified stated interest. Under these rules, a U.S. holder generally will have to include in taxable income increasingly greater amounts of OID in successive accrual periods.

The Notes will be treated as issued with OID for U.S. federal income tax purposes because the amount payable at maturity exceeds the issue price (90% of the principal amount, reduced by any portion of the purchase price allocated to the other Securities, and before taking into account the Company’s option to extend the Notes’ maturity) by more than a de minimis amount. Although payment of interest may be made annually upon the Notes’ maturity one year after issuance, due to the Company’s option to extend the Maturity Date by six months, which option would reduce the yield of the Notes, the Company will be deemed to exercise such option for purposes of determining whether the interest is qualified stated interest. Because interest would not be payable at least annually if the Company exercises its option to extend the Maturity Date, we intend to take the position that none of the payments on the Notes will constitute qualified stated interest. Based on this treatment, the amount of OID on the Notes will be equal to the difference between the amount payable at maturity and the issue price of the Notes. A U.S. holder, whether on the cash or accrual method for U.S. federal income tax purposes, must include any OID in gross income (as ordinary income) as the OID accrues (on a constant yield to maturity basis), regardless of whether cash attributable to that income is received at such time.

The OID rules do not apply to a short-term obligation, generally defined as an obligation with a fixed maturity date that is not more than one year from the date of issue. However, for this purpose, the maturity date of a debt instrument is the last possible date that the instrument could be outstanding under the terms of the instrument. Although the Notes have a term to maturity of one year after issuance, due to the Company’s option to extend the Maturity Date by six months, we intend to take the position that the Notes are not short-term obligations, and therefore are subject to the OID rules.

Additional Interest

We may be required to make payments of additional interest to a U.S. holder of the Notes if an event of default occurs. We believe that there is only a remote possibility that we would be required to pay additional interest, or that if such additional interest were required to be paid, it would be an incidental amount, and therefore we intend to take the position that this possible payment of additional interest will not subject the Notes to the special rules governing certain contingent payment debt instruments (which, if applicable, would affect the timing, amount and character of income with respect to the Notes). Our determination in this regard, while not binding on the IRS, is binding on a U.S. holder unless disclosure of a contrary position is made in the manner required by applicable Treasury regulations. The remainder of this discussion assumes that the Notes are not treated as contingent payment debt instruments. If, contrary to our expectations, we pay additional interest, although not free from doubt, such additional interest should be taxable to a U.S. holder as ordinary interest income at the time the additional interest accrues or is paid in accordance with the U.S. holder’s regular method of tax accounting. In the event we pay additional interest on the Notes, U.S. holders should consult their own tax advisors regarding the treatment of such amounts.

Sale, Exchange, Redemption or Other Taxable Disposition of the Notes

Assuming we do not constitute a PFIC for any taxable year, a U.S. holder generally will recognize capital gain or loss if the holder disposes of the Notes in a sale, exchange, redemption or other taxable disposition (other than conversion of the Notes into our common shares or into a combination of cash and our common shares, the U.S. federal income tax consequences of which are described under “—Conversion of the Notes” below). The U.S. holder’s gain or loss will equal the difference between the amount realized by the holder (other than amounts attributable to accrued but unpaid interest) and the holder’s tax basis in the Notes. The amount realized by the U.S. holder will include the amount of any cash and the fair market value of any other property received for the Notes. The U.S. holder’s tax basis in the Notes purchased in the initial offering generally will equal the adjusted issue price, as described in “—Taxation of Interest and Original Issue Discount” above. The portion of any amount realized that is attributable to accrued interest will not be taken into account in computing the U.S. holder’s capital gain or loss. Instead, that portion will be taxed as ordinary interest income as described above to the extent that the U.S. holder has not previously included the accrued interest in income. The gain or loss recognized by the U.S. holder on the disposition of the Notes generally will be long-term capital gain or loss if the holder has held the Notes for more than one year, or short-term capital gain or loss if the holder held the Notes for one year or less, at the time of the transaction. Long-term capital gain of non-corporate taxpayers generally is taxed at reduced rates. Short-term capital gain is taxed at ordinary income rates. The deductibility of capital losses is subject to limitations.

Conversion of the Notes

A U.S. holder generally will not recognize any income, gain or loss on the conversion of the Notes into our common shares, subject to the discussion under “—Constructive Distributions” below regarding the possibility that certain adjustments to the conversion rate of the Notes may be treated as a taxable dividend. The U.S. holder’s aggregate tax basis in the common shares will equal the U.S. holder’s tax basis in the Notes. The U.S. holder’s holding period in the common shares will include the holding period in the Notes. Any common shares received that are attributable to accrued and unpaid interest on the Notes not yet included in income by a U.S. holder will be taxed as ordinary income in the amount of such accrued interest.

Tax Treatment of the Pre-Funded Warrants

We believe that our Pre-Funded Warrants should be treated as our common shares for U.S. federal income tax purposes, rather than warrants. Assuming this position is upheld, no gain or loss should be recognized upon the exercise of a Pre-Funded Warrant and, upon exercise, the holding period of a Pre-Funded Warrant should carry over to the common share received. Similarly, the tax basis of a Pre-Funded Warrant should carry over to the common share received upon exercise, increased by the exercise price of $0.01 per share. However, our position is not binding on the IRS and the IRS may treat the Pre-Funded Warrants as warrants to acquire our common shares. You should consult your tax advisor regarding the U.S. federal tax consequences of an investment in the Pre-Funded Warrants. The remainder of this discussions assumes our Pre-Funded Warrants are properly treated as our common shares.

Exercise or Lapse of the Warrants

Except as discussed below with respect to the net exercise of a Warrant (referred to herein as a “cashless exercise”), upon the exercise of a Warrant, a U.S. holder will not recognize gain or loss and will have a tax basis in the common shares received equal to the U.S. holder’s tax basis in the Warrant plus the exercise price of the Warrant. The holding period for the common shares received pursuant to the exercise of a Warrant will begin on the date following the date of exercise and will not include the period during which the U.S. holder holds the Warrant. If a Warrant lapses unexercised, a U.S. holder will recognize a capital loss in an amount equal to the U.S. holder’s tax basis in the Warrant. The loss will be long-term capital loss if the Warrant has been held for more than one year as of the date the Warrant lapsed. The deductibility of capital losses is subject to certain limitations.

Under certain circumstances, upon the exercise of a Warrant, you may elect to settle the exercised Warrant pursuant to a cashless exercise (see “Description of the Warrants—Cashless Exercise” above). The tax consequences of a cashless exercise of a Warrant are not clear under current U.S. federal income tax law. A cashless exercise may be tax-free either because the exercise is not a gain recognition event or because the exercise is treated as a tax-free recapitalization for U.S. federal income tax purposes. Under either tax-free treatment approach, a U.S. holder’s tax basis in the common shares received on exercise of a Warrant equals the U.S. holder’s tax basis in the Warrant. If the cashless exercise is treated as a recapitalization, the holding period of the common shares received would include the holding period of the Warrant. If the cashless exercise is treated as not being a gain recognition event (and not a tax-free recapitalization), the holding period in the common shares received might be treated as commencing on the date following the date of exercise of the Warrants (and not include the holding period of the Warrant). We anticipate treating a cashless exercise of a Warrant as a tax-free recapitalization for U.S. federal income tax purposes.

A cashless exercise, however, might be treated as a taxable exchange in which gain or loss is recognized. In such event, a U.S. holder could be deemed to have exchanged a number of Warrants having a fair market value equal to the exercise price for the total number of Warrants exercised (including the Warrants deemed exchanged) for an amount of cash equal to such exercise price. In this case, a U.S. holder would recognize gain or loss in an amount equal to the difference between the fair market value of the Warrants deemed exchanged and surrendered to pay the exercise price and the U.S. holder’s tax basis in such Warrants. Alternatively, a U.S. holder might recognize gain or loss in an amount equal to the fair market value of all the Warrants surrendered in the exercise less the U.S. holder’s tax basis in such Warrants. In either such case, any such gain or loss would be capital gain or loss, and would be long-term capital gain or loss if the U.S. holder’s holding period of the Warrants at the time of the deemed exchange exceeds one year, and the U.S. holder’s tax basis in the common shares received would equal the sum of the U.S. holder’s tax basis in the total number of Warrants exercised (including the Warrants deemed exchanged) plus the amount of gain recognized in the deemed exchange. A U.S. holder’s holding period for the common shares received would commence on the date following the date of exercise of the Warrants.

Due to the absence of authority on the U.S. federal income tax treatment of a cashless exercise of warrants, we cannot give any assurance which, if any, of the alternative tax consequences and holding periods described above would be adopted by the IRS or a court. Accordingly, U.S. holders should consult their tax advisors regarding the tax consequences of a cashless exercise of the Warrants.

Constructive Distributions

Under Section 305 of the Code, an adjustment to (or a failure to adjust) the number of shares of common shares issuable upon exercise of a Warrant, or an adjustment to (or a failure to adjust) the exercise price of a Warrant, may be treated as a constructive distribution to a U.S. holder to the extent such adjustment (or failure to adjust) has the effect of increasing the U.S. holder’s proportionate interest in our earnings and profits or assets, as determined under U.S. federal income tax principles, depending on the circumstances of such adjustment (or failure to adjust) (for example, if such adjustment is to compensate for a distribution of cash or other property to our stockholders). Any such constructive dividend would be treated for U.S. federal income tax purposes in the same manner as an actual distribution on our common shares paid in cash or other property, as described below under “—Taxation of Distributions Paid on Common Shares,” regardless of whether an actual distribution of cash or other property occurs.

The terms of the Notes allow for changes in the conversion rate of the Notes under certain circumstances. A change in conversion rate that allows a U.S. holder to receive more shares of common shares on conversion may increase such holder’s proportionate interests in our earnings and profits or assets. In that case, a U.S. holder may be treated as having received a taxable distribution. A taxable constructive distribution would result, for example, if the conversion rate is adjusted to compensate a U.S. holder for distributions of cash or property to our stockholders. If an event occurs that dilutes the interests of stockholders or increases the interests of a U.S. holders of the Notes and the conversion rate of the Notes is not adjusted (or not adequately adjusted), this event also could result in a taxable constructive distribution to the U.S. holder. Conversely, if an event occurs that dilutes the interests of a U.S. holder of the Notes and the conversion rate is not adjusted (or not adequately adjusted), the resulting increase in the proportionate interests of our stockholders could be treated as a taxable constructive distribution to the stockholders.

Not all changes in the conversion rate that result in a U.S. holder of the Notes receiving more common shares on conversion, however, increase such holder’s proportionate interests in our earnings and profits or assets. For instance, a change in conversion rate could simply prevent the dilution of the holder’s interests upon a stock split or other change in capital structure. Changes of this type, if made pursuant to a bona fide reasonable adjustment formula, are not treated as taxable constructive stock distributions. Any taxable constructive distribution resulting from a change to, or failure to change, the conversion rate would be treated for U.S. federal income tax purposes in the same manner as an actual distribution on our common shares paid in cash or other property, as described above under “—Taxation of Distributions Paid on Common Shares.” Generally, a U.S. holder’s adjusted tax basis in the Notes will be increased to the extent of any such taxable constructive distribution that is treated as a dividend. U.S. holders should consult their own tax advisors regarding whether any taxable constructive dividends would be eligible for the reduced rates described below under “—Taxation of Distributions Paid on Common Shares” (for non-corporate holders), as the requisite applicable holding periods might not be considered to be satisfied. 

Taxation of Distributions Paid on Common Shares or Pre-Funded Warrants

Subject to the passive foreign investment company, or PFIC, rules discussed below, any distributions made by us with respect to our common shares or Pre-Funded Warrants to a U.S. holder will generally constitute dividends, which may be taxable as ordinary income or “qualified dividend income” as described in more detail below, to the extent of our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Distributions in excess of our earnings and profits will be treated first as a non-taxable return of capital to the extent of the U.S. holder’s tax basis in his or her common shares or Pre-Funded Warrants on a dollar-for-dollar basis and thereafter as capital gain. Because we are not a U.S. corporation, U.S. holders that are corporations will generally not be entitled to claim a dividends-received deduction with respect to any distributions they receive from us.

Dividends paid on common shares or Pre-Funded Warrants to a U.S. holder which is an individual, trust, or estate (a “U.S. Non-Corporate Holder”) will generally be treated as “qualified dividend income” that is taxable to such shareholders at preferential U.S. federal income tax rates provided that (1) the common shares are readily tradable on an established securities market in the United States (such as Nasdaq on which our common shares are listed); (2) we are not a PFIC for the taxable year during which the dividend is paid or the immediately preceding taxable year (which we do not expect to be); (3) the U.S. Non-Corporate Holder has owned the common shares or Pre-Funded Warrants for more than 60 days in the 121-day period beginning 60 days before the date on which the common shares or Pre-Funded Warrants become ex-dividend; and (4) certain other conditions are met.

Any dividends paid by us which are not eligible for these preferential rates will be taxed as ordinary income to a U.S. holder.

Special rules may apply to any “extraordinary dividend”—generally, a dividend in an amount which is equal to or in excess of 10% of a shareholder’s adjusted basis in a common share or Pre-Funded Warrant —paid by us. If we pay an “extraordinary dividend” on our common shares or Pre-Funded Warrants that is treated as “qualified dividend income,” then any loss derived by a U.S. Non-Corporate Holder from the sale or exchange of such common shares or Pre-Funded Warrants will be treated as long-term capital loss to the extent of such dividend.

Sale, Exchange or other Disposition of Common Shares Warrants or Pre-Funded Warrants

Assuming we do not constitute a PFIC for any taxable year, a U.S. holder generally will recognize taxable gain or loss upon a sale, exchange or other disposition of our common shares, Warrants or Pre-Funded Warrants in an amount equal to the difference between the amount realized by the U.S. holder from such sale, exchange or other disposition and the U.S. holder’s tax basis in such common shares, Warrants or Pre-Funded Warrants. Such gain or loss will be treated as long-term capital gain or loss if the U.S. holder’s holding period in the common shares, Warrants or Pre-Funded Warrants is greater than one year at the time of the sale, exchange or other disposition. A U.S. holder’s ability to deduct capital losses is subject to certain limitations.

Passive Foreign Investment Company Rules

Special U.S. federal income tax rules apply to a U.S. holder that holds stock or is treated as holding stock by application of certain attribution rules (for instance, treating warrants as stock) in a foreign corporation classified as a PFIC for U.S. federal income tax purposes. In general, we will be treated as a PFIC with respect to a U.S. holder if, for any taxable year in which such holder held our common shares, Warrants, Pre-Funded Warrants or possibly Notes, either:

For purposes of determining whether we are a PFIC, we will be treated as earning and owning our proportionate share of the income and assets, respectively, of any of our subsidiary companies in which we own at least 25% of the value of the subsidiary’s stock or other ownership interest. Income earned, or deemed earned, by us in connection with the performance of services should not constitute passive income. By contrast, rental income, which includes bareboat hire, would generally constitute “passive income” unless we are treated under specific rules as deriving rental income in the active conduct of a trade or business.

We believe that our predecessor was not a PFIC for our 2025 taxable year and we do not expect to be treated as a PFIC in the current or subsequent taxable years. Although there is no legal authority directly on point, our belief is based principally on the position that, for purposes of determining whether we are a PFIC, the gross income we derive or are deemed to derive from the time chartering and voyage chartering activities of our wholly-owned subsidiaries should constitute services income, rather than rental income. Correspondingly, we believe that such income does not constitute passive income, and the assets that we or our wholly-owned subsidiaries own and operate in connection with the production of such income, in particular vessels, do not constitute passive assets for purposes of determining whether we are a PFIC. We believe there is substantial legal authority supporting our position consisting of case law and IRS pronouncements concerning the characterization of income derived from time charters and voyage charters as services income for other tax purposes. However, there is also authority which characterizes time charter income as rental income rather than services income for other tax purposes. It should be noted that in the absence of any legal authority specifically relating to the statutory provisions governing PFICs, the IRS or a court could disagree with this position. In addition, although we intend to conduct our affairs in a manner so as to avoid being classified as a PFIC with respect to any taxable year, there can be no assurance that the nature of our operations will not change in the future.

As discussed more fully below, if we were to be treated as a PFIC for any taxable year, a U.S. holder would be subject to different taxation rules depending on whether the U.S. holder makes an election to treat us as a “Qualified Electing Fund,” which election is referred to as a “QEF election.” As an alternative to making a QEF election, a U.S. holder should be able to make a “mark-to-market” election with respect to the common shares or Pre-Funded Warrants, as discussed below. In addition, if we were to be treated as a PFIC, a U.S. holder would be required to file an IRS Form 8621 with respect to such holder’s common shares, Warrants, Pre-Funded Warrants and possibly Notes.

Taxation of U.S. Holders Making a Timely QEF Election

If a U.S. holder of our common shares or Pre-Funded Warrants makes a timely QEF election, which U.S. holder is referred to as an “Electing Holder,” the Electing Holder must report each year for U.S. federal income tax purposes its pro rata share of our ordinary earnings and its net capital gain, if any, for our taxable year that ends with or within the taxable year of the Electing Holder, regardless of whether or not distributions were received from us by the Electing Holder. The Electing Holder’s adjusted tax basis in the common shares or Pre-Funded Warrants will be increased to reflect taxed but undistributed earnings and profits. Distributions of earnings and profits that had been previously taxed will result in a corresponding reduction in the adjusted tax basis in the common shares or Pre-Funded Warrants and will not be taxed again once distributed. An Electing Holder would generally recognize capital gain or loss on the sale, exchange or other disposition of the common shares or Pre-Funded Warrants. A U.S. holder would make a QEF election with respect to any year that we are a PFIC by filing IRS Form 8621 with its U.S. federal income tax return. After the end of each taxable year, we will determine whether we were a PFIC for such taxable year. If we determine or otherwise become aware that we are a PFIC for any taxable year, we will use commercially reasonable efforts to provide each U.S. holder with all necessary information, including a PFIC Annual Information Statement, in order to enable such holder to make a QEF election for such taxable year. A U.S. holder of Warrants or Notes will not be able to make a QEF election in respect of such Warrants or Notes.

Taxation of U.S. Holders Making a “Mark-to-Market” Election

Alternatively, if we were to be treated as a PFIC for any taxable year and, as anticipated, our common shares are treated as “marketable stock,” a U.S. holder of our common shares or Pre-Funded Warrants would be allowed to make a “mark-to-market” election with respect to our common shares or Pre-Funded Warrants. If that election is made, the U.S. holder generally would include as ordinary income in each taxable year the excess, if any, of the fair market value of the common shares or Pre-Funded Warrants at the end of the taxable year over such U.S. holder’s adjusted tax basis in the common shares or Pre-Funded Warrants. The U.S. holder would also be permitted an ordinary loss in respect of the excess, if any, of the U.S. holder’s adjusted tax basis in the common shares or Pre-Funded Warrants over its fair market value at the end of the taxable year, but only to the extent of the net amount previously included in income as a result of the mark-to-market election. A U.S. holder’s tax basis in its common shares or Pre-Funded Warrants would be adjusted to reflect any such income or loss amount. Gain realized on the sale, exchange or other disposition of the common shares or Pre-Funded Warrants would be treated as ordinary income, and any loss realized on the sale, exchange or other disposition of the common shares or Pre-Funded Warrants would be treated as ordinary loss to the extent that such loss does not exceed the net mark-to-market gains previously included by the U.S. holder. A U.S. holder of Warrants or Notes will not be able to make a mark-to-market election in respect of such Warrants or Notes.

Taxation of U.S. Holders Not Making a Timely QEF or Mark-to-Market Election

Finally, if we were to be treated as a PFIC for any taxable year, a U.S. holder who does not make either a QEF election or a “mark-to-market” election for that year, whom we refer to as a “Non-Electing Holder,” would be subject to special rules with respect to (1) any excess distribution (i.e., the portion of any distributions received by the Non-Electing Holder on our common shares or Pre-Funded Warrants in a taxable year in excess of 125 percent of the average annual distributions received by the Non-Electing Holder in the three preceding taxable years, or, if shorter, the Non-Electing Holder’s holding period for our common shares or Pre-Funded Warrants), and (2) any gain realized on the sale, exchange or other disposition of our common shares, Warrants or Pre-Funded Warrants. Under these special rules:

These penalties would not apply to a pension or profit-sharing trust or other tax-exempt organization that did not borrow funds or otherwise utilize leverage in connection with its acquisition of our common shares, Warrants or Pre-Funded Warrants. If a Non-Electing Holder who is an individual dies while owning our common shares, Warrants or Pre-Funded Warrants, such Non-Electing Holder’s successor generally would not receive a step-up in tax basis with respect to such common shares, Warrants or Pre-Funded Warrants.

The treatment of Notes under the PFIC rules is subject to uncertainty. The Notes may be subject to the same tax treatment as the Warrants. Investors are urged to consult their tax advisors regarding the applicability of PFIC rules to the Notes.

Net Investment Income Tax

A U.S. holder that is an individual or estate, or a trust that does not fall into a special class of trusts that is exempt from such tax, is subject to a 3.8% tax on the lesser of (1) such U.S. holder’s “net investment income” (or undistributed “net investment income” in the case of estates and trusts) for the relevant taxable year and (2) the excess of such U.S. holder’s modified adjusted gross income for the taxable year over a certain threshold (which in the case of individuals will be between $125,000 and $250,000, depending on the individual’s circumstances). A U.S. holder’s net investment income will generally include its gross dividend income and its net gains from the disposition of the common shares, Warrants, Pre-Funded Warrants or Notes, unless such dividends or net gains are derived in the ordinary course of the conduct of a trade or business (other than a trade or business that consists of certain passive or trading activities). Net investment income generally will not include a U.S. holder’s pro rata share of our income and gain (if we are a PFIC and that U.S. holder makes a QEF election, as described above in “—Taxation of U.S. holders Making a Timely QEF Election”). However, a U.S. holder may elect to treat inclusions of income and gain from a QEF election as net investment income. Failure to make this election could result in a mismatch between a U.S. holder’s ordinary income and net investment income. If you are a U.S. holder that is an individual, estate or trust, you are urged to consult your tax advisor regarding the applicability of the net investment income tax to your income and gains in respect of your investment in our common shares, Warrants, Pre-Funded Warrants or Notes.

United States Federal Income Taxation of Non-U.S. Holders

Dividends paid to a Non-U.S. holder with respect to our common shares or Pre-Funded Warrants generally should not be subject to U.S. federal income tax, unless the dividends are effectively connected with the Non-U.S. holder’s conduct of a trade or business within the United States (and, if required by an applicable income tax treaty, are attributable to a permanent establishment or fixed base that such holder maintains in the United States).

In addition, a Non-U.S. holder generally should not be subject to U.S. federal income tax on any gain attributable to a sale or other disposition of our common shares, Warrants, Pre-Funded Warrants or Notes unless such gain is effectively connected with its conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, is attributable to a permanent establishment or fixed base that such holder maintains in the United States) or the Non-U.S. holder is an individual who is present in the United States for 183 days or more in the taxable year of sale or other disposition and certain other conditions are met (in which case such gain from United States sources may be subject to tax at a 30% rate or a lower applicable tax treaty rate).

Dividends and gains that are effectively connected with the Non-U.S. holder’s conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, are attributable to a permanent establishment or fixed base in the United States) generally should be subject to tax in the same manner as for a U.S. holder and, if the Non-U.S. holder is a corporation for U.S. federal income tax purposes, it also may be subject to an additional branch profits tax at a 30% rate or a lower applicable tax treaty rate.

A Non-U.S. holder will generally not be subject to U.S. federal income tax upon the exercise or lapse of our Warrants, or upon the conversion of the Notes.

Backup Withholding and Information Reporting

In general, information reporting for U.S. federal income tax purposes should apply to distributions made on our common shares or Pre-Funded Warrants within the United States to a non-corporate U.S. holder and to the proceeds from sales and other dispositions of our common shares, Warrants, Pre-Funded Warrants or Notes to or through a U.S. office of a broker by a non-corporate U.S. holder. Payments made (and sales and other dispositions effected at an office) outside the United States will be subject to information reporting in limited circumstances.

In addition, backup withholding of U.S. federal income tax, currently at a rate of 24%, generally should apply to distributions paid on our common shares or Pre-Funded Warrants to a non-corporate U.S. holder and the proceeds from sales and other dispositions of our common shares, Warrants, Pre-Funded Warrants or Notes by a non-corporate U.S. holder, who:

A Non-U.S. holder generally may eliminate the requirement for information reporting and backup withholding by providing certification of its foreign status, under penalties of perjury, on a duly executed applicable IRS Form W-8 or by otherwise establishing an exemption.

Backup withholding is not an additional tax. Rather, the amount of any backup withholding generally should be allowed as a credit against a U.S. holder’s or a Non-U.S. holder’s U.S. federal income tax liability and may entitle such holder to a refund, provided that certain required information is timely furnished to the IRS.

Individuals who are U.S. holders (and to the extent specified in applicable Treasury regulations, certain individuals who are Non-U.S. holders and certain U.S. entities) who hold “specified foreign financial assets” (as defined in Section 6038D of the Code) are required to file IRS Form 8938 with information relating to the asset for each taxable year in which the aggregate value of all such assets exceeds $75,000 at any time during the taxable year or $50,000 on the last day of the taxable year (or such higher dollar amount as prescribed by applicable Treasury regulations). Specified foreign financial assets would include, among other assets, our common shares, Warrants, Pre-Funded Warrants and Notes unless the common shares, Warrants, Pre-Funded Warrants or Notes are held through an account maintained with a U.S. financial institution. Substantial penalties apply to any failure to timely file IRS Form 8938, unless the failure is shown to be due to reasonable cause and not due to willful neglect. Additionally, in the event an individual U.S. holder (and to the extent specified in applicable Treasury regulations, an individual Non-U.S. holder or a U.S. entity) that is required to file IRS Form 8938 does not file such form, the statute of limitations on the assessment and collection of U.S. federal income taxes of such holder for the related tax year may not close until three years after the date that the required information is filed. U.S. holders (including U.S. entities) and Non-U.S. holders are encouraged to consult their own tax advisors regarding their reporting obligations under this legislation.

Marshall Islands Tax Consequences

The following represents the opinion of our Marshall Islands counsel, Watson Farley & Williams LLP, and is a summary of the material Marshall Islands tax consequences of the ownership and disposition of the Securities.

We are incorporated in the Republic of the Marshall Islands. Under current Marshall Islands law, we are not subject to tax on income or capital gains, no Marshall Islands withholding tax will be imposed upon payment of dividends by us to our shareholders, and holders of our Warrants, Pre-Funded Warrants, Notes, Commitment Shares and other common shares that are not residents of or domiciled or carrying on any commercial activity in the Republic of the Marshall Islands will not be subject to Marshall Islands tax on the sale or other disposition of our Warrants, Pre-Funded Warrants, Notes, Commitment Shares and other common shares.

EXPENSES RELATING TO THIS OFFERING

Set forth below is an itemization of the total expenses, excluding Placement Agent fees, expected to be incurred in connection with the offer and sale of our securities.

LEGAL MATTERS

Certain legal matters with respect to United States Federal and New York law and Marshall Islands law in connection with this offering will be passed upon for us by Watson Farley & Williams LLP, New York, New York. The Placement Agent is being represented by Ellenoff Grossman & Schole 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.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The Commission allows us to “incorporate by reference” information that we file with it. 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 supplement, and information that we file later with the Commission prior to the termination of this offering will also be considered to be part of this prospectus supplement and will automatically update and supersede previously filed information, including information contained in this document.

This prospectus supplement incorporates by reference the following documents:

We are also incorporating by reference all subsequent annual reports on Form 20-F that we file with the Commission and certain reports on Form 6-K that we furnish to the Commission after the date of this prospectus supplement (if they state that they are incorporated by reference into the registration statement of which this prospectus supplement is a part) until we file a post-effective amendment indicating that the offering of the securities made by this prospectus supplement has been terminated. In all cases, you should rely on the later information over different information included in this prospectus supplement or the accompanying prospectus.

You should rely only on the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. We have not, and the Placement Agent has 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 Placement Agent is 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 supplement and the accompanying prospectus as well as the information we previously filed with the Commission 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.

You may request a paper copy of our Commission filings, at no cost, 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)

These reports may also be obtained on our website at https://rubicoinc.com. None of the information on our website is a part of this prospectus supplement or the accompanying prospectus.

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.

WHERE YOU CAN FIND MORE INFORMATION

As required by the Securities Act, we filed a registration statement relating to the securities offered by this prospectus supplement with the Commission. This prospectus supplement is a part of that registration statement, which includes additional information.

Government Filings

We file annual and special reports within the Commission. The Commission maintains a website (http://www.sec.gov) that contains reports, proxy and information statements and other information regarding registrants that file electronically with the Commission. Our filings are also available on our website at https://rubicoinc.com. The information on our website, however, is not, and should not be deemed to be, a part of this prospectus supplement. Further, other than as described below, the information contained in or accessible from the Commission’s website is not part of this prospectus supplement.

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.

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 July 14, 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)

$15,000,000 Principal Amount of Senior Convertible Notes,

Common Share Purchase Warrants,

Pre-Funded Warrants,

Common Shares Underlying the Senior Convertible Notes, Common Share Purchase Warrants, and

Pre-Funded Warrants,

and

Common Shares Issuable as Commitment Shares

Rubico Inc.

PROSPECTUS SUPPLEMENT

Maxim Group LLC

The date of this prospectus supplement is October 16, 2026