C3is Inc.: 5%+ holders

As of November 7, 2026, 7 holders' latest Schedule 13D or 13G filings report owning 5% or more of C3is Inc. The largest reported stake is Imperial Petroleum Inc.'s, at 80.5%. 36 filings are on record since September 24, 2025 (Schedule 13D/A, August 28, 2026).

Who owns C3is Inc.?

HORNE TIMOTHY P also filed stake reports on 1 other company ↓

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Key facts

• Filing 2026-11-06 · Reporting person: Jane Street Group, LLC · Sole voting: 0 · Shared voting: 16,992 · Sole dispositive: 0 · Shared dispositive: 16,992 · SCHEDULE 13G/A, 2026-11-06
• Filing 2026-10-05 · Reporting person: Alta Partners LLC · Sole voting: 46,773 · Shared voting: 0 · Sole dispositive: 46,773 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-10-05
• Filing 2026-10-05 · Reporting person: Ascent Partners Fund LLC · Sole voting: 0 · Shared voting: 0 · Sole dispositive: 0 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-10-05
• Filed 2026-10-02 · Holder: Towerview LLC · SCHEDULE 13G/A
• Filing 2026-09-03 · Reporting person: Horne Timothy P · Sole voting: 135,000 · Shared voting: 0 · Sole dispositive: 135,000 · Shared dispositive: 0 · SCHEDULE 13G, 2026-09-03

C3is Inc. has 36 Schedule 13D or 13G filings on record since 2025-09-24. 7 holders' latest filing reports 5% or more of common stock, par value $0.01 per share. Each figure below is the holder's own, as filed, with the filing linked.

Holders

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More on C3is Inc. and the records around it.

C3is Inc. elsewhere on the record

• Who owns it

Companies that share a holder

• HORNE TIMOTHY P also filed stake reports on 1 other company: WATTS WATER TECHNOLOGIES INC (Oct 2026)
• TOWERVIEW LLC also filed stake reports on 1 other company: STEALTHGAS INC. (Jul 2026)
• Evergreen Capital Management LLC also filed stake reports on 2 other companies: BlockchAIn Digital Infrastructure, Inc. (May 2026), Signing Day Sports, Inc. (Jan 2026)

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Voting and dispositive power, as filed

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The latest filing identifies C3is Inc. by CUSIP Y18284409 and gives its principal executive office as 331 KIFISSIAS AVENUE, ATHENS (SCHEDULE 13G/A, 2026-11-06).

Source of funds (Item 3)

Item 3 of the statement is hereby amended by adding the following paragraphs to the end of Item 3: This Amendment No. 13 updates the number of shares of Common Stock beneficially owned by Imperial Petroleum as a result of changes in the conversion price of the 5.0% Series A Cumulative Convertible Perpetual Preferred Stock, par value $0.01 per share (the "Series A Convertible Preferred Stock"), of the Issuer.Imperial Petroleum Inc., SCHEDULE 13D/A, 2026-08-28

Purpose of Transaction (Item 4)

Flawless Management Inc.

The Reporting Persons acquired the securities described in this Schedule 13D for investment purposes and intend to review their investment in the Issuer on a continuing basis. Any Reporting Person may from time to time acquire additional securities of the Issuer, or retain or sell all or a portion of the shares then held by the Reporting Persons, in the open market, block trades, underwritten public offerings or privately negotiated transactions. Any actions any Reporting Person might undertake with respect to its investment in the Issuer may be made at any time and from time to time and will be dependent upon such Reporting Person's review of numerous factors, including, but not limited to: ongoing evaluation of the Issuer's business, financial condition, operations, prospects and strategic alternatives; price levels of the Issuer's securities; general market, industry and economic conditions; the relative attractiveness of alternative business and investment opportunities; tax considerations; liquidity of the Issuer's securities; and other factors and future developments. Mr. Vafias serves as the Non-Executive Chairman of the Issuer and therefore regularly engages in discussions with management of the Issuer, the board of directors of the Issuer, other shareholders of the Issuer and other relevant parties, which discussions may include matters ranging from the operations and conduct of the Issuer's business to considering or exploring extraordinary corporate transactions …The first part of Item 4 of the SCHEDULE 13D/A filed 2025-10-10; the filing has the rest

Imperial Petroleum Inc.

The Reporting Person involved in the securities described in this Schedule 13D in connection with the Spin-Off Distribution, and intends to review its investment in the Issuer on a continuing basis. The Reporting Person may from time to time acquire additional securities of the Issuer, or retain or sell all or portion of the shares then held by the Reporting Person, in the open market, block trades, underwritten public offerings or privately negotiated transactions. Any actions the Reporting Person might undertake with respect to its investment in the Issuer may be made at any time and from time to time and will be dependent upon the Reporting Person's review of numerous factors, including, but not limited to: ongoing evaluation of the Issuer's business, financial condition, operations, prospects and strategic alternatives; price levels of the Issuer's securities; general market, industry and economic conditions; the relative attractiveness of alternative business and investment opportunities; tax considerations; liquidity of the Issuer's securities; and other factors and future developments. Mr. Vafias serves as the Non-Executive Chairman of the Issuer and John Kostoyannis and George Xiradakis each serve as a director of the Issuer, other shareholders of the Issuer and other relevant parties, which discussions may include matters ranging from the operations and conduct of the Issuer's business to considering or exploring extraordinary corporate transactions including the …The first part of Item 4 of the SCHEDULE 13D/A filed 2026-08-28; the filing has the rest

Timeline

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Questions about who owns C3is Inc.

Who owns C3is Inc.?

On this page, 7 holders' latest ownership filings report 5% or more of C3is Inc.: Imperial Petroleum Inc. (80.5%, Schedule 13D/A, filed 2026-08-28), Ayrton Capital LLC (9.99%, Schedule 13G, filed 2026-02-11), Lind Global Fund III LP (9.99%, Schedule 13G, filed 2026-07-31), CVI Investments, Inc. (9.9%, Schedule 13G, filed 2026-08-03) and Horne Timothy P (9.1%, Schedule 13G, filed 2026-09-03); 2 more are listed above.

Who are the largest shareholders of C3is Inc.?

By the share each holder's latest filing reports, the largest holders of C3is Inc. on this page are Imperial Petroleum Inc. (80.5%), Ayrton Capital LLC (9.99%) and Lind Global Fund III LP (9.99%).

When did Imperial Petroleum Inc. buy into C3is Inc.?

The filings give report dates, not purchase dates. The earliest filing from Imperial Petroleum Inc. on this page is the Schedule 13D/A, filed 2025-10-10, reporting 68.8%; its latest, Schedule 13D/A filed 2026-08-28, reports 80.5%. That earliest filing is itself an amendment, which updates an earlier report.

Is this an audit or a full list?

Neither. The ownership list on this page covers only Schedule 13D and 13G filings, which holders make once they own 5% or more of a class of shares (an amendment can report a stake that has since fallen below 5%); 36 such filings are shown here. It is not an audit and not a full cap table: holders who never reached 5% are not listed, and a stake can change after its latest filing.

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Where this comes from

Anyone who comes to own more than 5% of a class of a listed company's voting shares has to tell the SEC. A holder who may seek to change or influence the company files Schedule 13D, and has to say in Item 4, "Purpose of Transaction", what it intends to do. A holder with no such intent, such as many index and passive funds, may file the shorter Schedule 13G. Both are amended when the stake changes, including when it falls below 5%.

Every row here is one of those filings, linked to the filing itself. Percentages and share counts are exactly as the holder filed them, for the holder the filing names; an amendment showing a lower figure is shown as filed. Item 4 text is quoted word for word. Where a 13D's Item 4 contains a sentence stating a definite intent to influence the company, that sentence is marked and quoted; the page does not describe the holder or its motives beyond the words it filed. Nothing here is investment advice.

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