Exhibit 99.1

C3is Inc. Announces Pricing of $2 Million Registered Direct Offering

ATHENS, GREECE, October 8, 2025 — C3is Inc. (NASDAQ: CISS) (the “Company”), a ship-owning company providing dry bulk and tanker seaborne transportation services, today announced that it has entered into definitive agreements in a registered direct offering with institutional investors for the purchase and sale of 800,000 shares of its Common Stock at a public offering price of $2.50, for an aggregate offering price of $2.0 million.

Aggregate gross proceeds to the Company are expected to be approximately $2.0 million. The transaction is expected to close on or about October 9, 2025, subject to the satisfaction of customary closing conditions. The Company expects to use the net proceeds from the offering, together with its existing cash, for general corporate purposes and working capital.

Aegis Capital Corp. is acting as exclusive placement agent for the offering. Goodwin Procter LLP is acting as U.S. counsel to the Company. Kaufman & Canoles, P.C. is acting as U.S. counsel to Aegis Capital Corp.

The registered direct offering is being made pursuant to an effective shelf registration statement on Form F-3 (No. 333-285135) previously filed with the U.S. Securities and Exchange Commission (SEC) and declared effective by the SEC on March 6, 2025. A final prospectus supplement and accompanying prospectus describing the terms of the proposed offering will be filed with the SEC and will be available on the SEC’s website located at www.sec.gov. Electronic copies of the final prospectus supplement and the accompanying prospectus may be obtained, when available, by contacting Aegis Capital Corp., Attention: Syndicate Department, 1345 Avenue of the Americas, 27th floor, New York, NY 10105, by email at syndicate@aegiscap.com, or by telephone at +1 (212) 813-1010.

Interested parties should read in their entirety the prospectus supplement and the accompanying prospectus and the other documents that the Company has filed with the SEC that are incorporated by reference in such prospectus supplement and the accompanying prospectus, which provide more information about the Company and such offering.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About C3is Inc.

C3is Inc. is a ship-owning company providing dry bulk and crude oil seaborne transportation services. The Company owns four vessels, three handysize drybulk carriers with a total capacity of 97,664 deadweight tons (dwt) and an Aframax oil tanker with a cargo carrying capacity of approximately 115,800 dwt, resulting with a fleet total capacity of 213,464 dwt. C3is Inc.’s shares of Common Stock are listed on the Nasdaq Capital Market and trade under the symbol “CISS.”

Forward-Looking Statements

The foregoing material may contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, each as amended. Forward-looking statements include all statements that do not relate solely to historical or current facts, including without limitation statements those related to the completion and timing of the offering and the intended use of the proceeds., and can be identified by the use of words such as “may,” “will,” “expect,” “project,” “estimate,” “anticipate,” “plan,” “believe,” “potential,” “should,” “continue” or the negative versions of those words or other comparable words. Forward-looking statements are not guarantees of future actions or performance. These forward-looking statements are based on information currently available to the Company and its current plans or expectations and are subject to a number of risks and uncertainties that could significantly affect current plans. Should one or more of these risks or uncertainties materialize, or the underlying assumptions prove incorrect, actual results may differ significantly from those anticipated, believed, estimated, expected, intended, or planned. Although the Company believes that the expectations reflected in the forward-looking statements are reasonable, the Company cannot guarantee future results, performance, or achievements. Except as required by applicable law, including the securities laws of the United States, the Company does not intend to update any of the forward-looking statements to conform these statements to actual results.

Nina Pyndiah

Chief Financial Officer

C3is INC.

00-30-210-6250-001

E-mail: info@c3is.pro

C3is Inc. 6-K