C3is (NASDAQ: CISS) adds 2011 product tanker in $22.9M deal

Rhea-AI Filing Summary

C3is Inc. filed a prospectus supplement that incorporates a new Form 6-K detailing an agreement to acquire a 2011 South Korean-built product tanker with 47,203 dwt capacity for $22.9 million from an entity affiliated with Brave Maritime Corp Inc. The deal with this related party was approved by the Company’s independent directors, who relied on independent vessel valuations and used the average valuation price.

The vessel is expected to be delivered between Q1 and Q2 2026, and C3is has the option to pay the purchase price one year after the purchase agreement date without interest. After delivery of this tanker and a previously announced pending product tanker acquisition, the Company’s fleet is expected to total six vessels with an aggregate capacity of 310,667 dwt across drybulk, Aframax oil, and product tanker segments.

Insights

Shipping sector and capital markets analyst

C3is adds a $22.9M product tanker, expanding fleet diversification.

C3is Inc. agreed to buy a 2011-built product tanker with 47,203 dwt capacity for $22.9 million from an entity affiliated with Brave Maritime. The purchase from an affiliate was vetted and approved by independent directors using third-party vessel valuations, which may help address governance and pricing concerns often associated with related-party deals.

The vessel is expected to be delivered between Q1 and Q2 2026, and C3is can defer payment for one year after the purchase agreement date without interest, which may support near-term liquidity. Assuming completion of this and a previously announced product tanker acquisition, the fleet would grow to six vessels totaling 310,667 dwt, increasing exposure to both drybulk and tanker markets.

FAQ

What transaction did C3is Inc. (CISS) disclose in this filing?

C3is Inc. disclosed an agreement to acquire a 2011 South Korean-built product tanker with 47,203 dwt capacity for $22.9 million from an entity affiliated with Brave Maritime Corp Inc.

How will the new tanker affect C3is Inc. (CISS) fleet size and capacity?

After delivery of this tanker and another previously announced product tanker, C3is Inc.’s fleet is expected to total 6 vessels with an aggregate capacity of 310,667 dwt across drybulk, Aframax oil, and product tanker segments.

When is the newly acquired C3is Inc. (CISS) tanker expected to be delivered?

The newly acquired product tanker is expected to be delivered to C3is Inc. between Q1 and Q2 2026.

How will C3is Inc. (CISS) pay for the $22.9 million tanker?

C3is Inc. has the option to pay the $22.9 million purchase price for the tanker one year after the date of the purchase agreement, without interest.

Was the related-party tanker deal at C3is Inc. (CISS) independently reviewed?

Yes. The transaction with Brave Maritime, which is affiliated with members of the Vafias family, was approved by the independent directors of C3is Inc., who obtained independent vessel valuations and used the average of these valuations.

How is this Form 6-K used in C3is Inc. (CISS) registration statements?

The Form 6-K is incorporated by reference into C3is Inc.’s Form S-8 (Reg. No. 333-273306) and Form F-3 (Reg. No. 333-285135), and is also attached to the prospectus supplement to the Form F-1 registration statement.

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Accepted by SEC EDGAR 01/20/2026 - 04:59 PM Learn about SEC filing dates

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-290011

PROSPECTUS SUPPLEMENT NO. 2

(TO PROSPECTUS DATED DECEMBER 11, 2025)

C3IS INC.

This is a supplement (“Prospectus Supplement”) to the prospectus, dated December 11, 2025 (“Prospectus”), of C3is Inc. (the “Company”), which forms a part of the Company’s Registration Statement on Form F-1 (Registration No. 333-272939), as amended or supplemented from time to time. This Prospectus Supplement is being filed to update and supplement the information included in the Prospectus with the information contained in our Reports on Form 6-K, furnished to the U.S. Securities and Exchange Commission on January 20, 2026 (the “Form 6-K”). Accordingly, we have attached the Form 6-K to this Prospectus Supplement.

This Prospectus Supplement should be read in conjunction with, and delivered with, the Prospectus and is qualified by reference to the Prospectus except to the extent that the information in this Prospectus Supplement supersedes the information contained in the Prospectus. This Prospectus Supplement is not complete without, and may not be delivered or utilized except in connection with, the Prospectus, including any amendments or supplements to it.

Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page 14 of the Prospectus for a discussion of information that should be considered in connection with an investment in our securities.

Neither the 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 supplement is January 20, 2026.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of January 2026

Commission File Number 001-41717

C3IS INC.

(Translation of registrant’s name into English)

331 Kifissias, Avenue Kifissia 14561 Athens, Greece

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F ☒   Form  40-F ☐

INFORMATION CONTAINED IN THIS FORM 6-K REPORT

Vessel Acquisition Agreement

C3is Inc. (the “Company”) has entered into an agreement to acquire a 2011 South Korean-built product tanker with 47,203 deadweight tons (dwt) capacity for a purchase price of $22.9 million, from an entity affiliated with Brave Maritime Corp Inc. The transaction with Brave Maritime, which is affiliated with members of the Vafias family, was approved by the independent directors of the Company, which obtained independent valuations of the vessel, and used the average price of these valuations.

The vessel is expected to be delivered between Q1 and Q2 2026. The Company has the option to pay for the vessel one year after the date of the purchase agreement, without interest.

Following this vessel delivery, and assuming no further acquisitions or dispositions other than the pending product tanker acquisition previously announced, the Company’s fleet will total 6 vessels, three Handysize drybulk carriers with a total capacity of 97,664 dwt, an Aframax oil tanker with a capacity of approximately 115,800 dwt and two product tankers with a capacity of approximately 97,203 dwt, resulting in a fleet total capacity of 310,667 dwt.

*****

This report on Form 6-K is hereby incorporated by reference into the Company’s Registration Statement on Form S-8 (Reg. No. 333-273306) filed with the Securities and Exchange Commission on July 18, 2023 and Registration Statement on Form F-3 (Reg. No. 333- 285135) filed with the Securities and Exchange Commission on February 21, 2025.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: January 20, 2026

C3IS INC.
By:		/s/ Nina Pyndiah
Name:		Nina Pyndiah
Title:		Chief Financial Officer