C3is (NASDAQ: CISS) files Form 6-K with preliminary Q3 2025 results

Rhea-AI Filing Summary

C3is Inc. filed a Form 6-K to furnish a press release announcing its financial and operating results for the three and nine months ended September 30, 2025. The results are described as preliminary and cover both 2025 and 2024 comparison periods.

The company notes that its independent accountants have not compiled, examined, or performed procedures on these preliminary results and provide no assurance on them. Most of the information in this Form 6-K, including Exhibit 99.1 other than the CEO commentary section, is incorporated by reference into C3is Inc.’s existing Form S-8 and Form F-3 registration statements.

Form 6-K: How Foreign Companies Report to the SEC →

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 November 2025

Commission File Number 001-41717

C3IS INC.

(Translation of registrant’s name into English)

331 Kifissias Avenue Erithrea 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

Financial and Operating Results for the three and nine months ended September 30, 2025

Attached to this report on Form 6-K as Exhibit 99.1 is a copy of C3is Inc.’s (the “Company”) press release, dated November 18, 2025, announcing its financial and operating results for the three and nine months ended September 30, 2025.

EXHIBIT INDEX

99.1 Press Release dated November 18, 2025

*****

Neither C3is Inc.’s independent accountants, nor any other independent accountants, have compiled, examined, or performed any procedures with respect to the preliminary financial results for the three and nine months ended September 30, 2025 and 2024, nor have they expressed any opinion or any other form of assurance on such information, and assume no responsibility for, and disclaim any association with, the preliminary financial results.

This report on Form 6-K, including exhibit 99.1 hereto other than the section entitled “CEO Dr. Diamantis Andriotis Commented:”, 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: November 18, 2025

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

FAQ

What does C3is Inc. (CISS) disclose in this Form 6-K?

C3is Inc. furnishes a press release as Exhibit 99.1 that announces its financial and operating results for the three and nine months ended September 30, 2025.

Are the C3is Inc. Q3 2025 results audited?

No. The company states that its independent accountants have not compiled, examined, or performed any procedures on the preliminary financial results and provide no opinion or assurance on them.

Which periods do C3is Inc.’s preliminary results cover in this filing?

The preliminary financial results relate to the three and nine months ended September 30, 2025 and 2024.

How is this C3is Inc. Form 6-K used in relation to existing registration statements?

The information in this Form 6-K, including Exhibit 99.1 other than the CEO commentary section, is incorporated by reference into C3is Inc.’s Form S-8 (Reg. No. 333-273306) and Form F-3 (Reg. No. 333-285135) registration statements.

Who signed the C3is Inc. Form 6-K for the Q3 2025 results?

The Form 6-K was signed on behalf of C3is Inc. by Nina Pyndiah, the company’s Chief Financial Officer.

Does the Form 6-K include the full financial tables for C3is Inc.?

The document indicates that detailed financial and operating results are contained in the press release attached as Exhibit 99.1, which is referenced but not reproduced in this excerpt.