[6-K] C3is Inc. Current Report (Foreign Issuer)

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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 August 2025

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 ☐

EXHIBIT INDEX

99.1		Proxy Statement for the 2025 Annual Meeting of Stockholders
99.2		Proxy and Notice Cards for the 2025 Annual Meeting of Stockholders
99.3		2024 Annual Report

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: August 29, 2025

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