5.02% C3is (NASDAQ: CISS) stake reported by Athanasios Tsiakmakis

Rhea-AI Filing Summary

C3is Inc. shareholder updates 5.02% ownership stake. Athanasios Tsiakmakis filed Amendment No. 1 to a Schedule 13G/A reporting beneficial ownership of 400,000 shares of C3is Inc. common stock, representing 5.02% of the class as of an event dated 01/09/2026. The percentage is based on 7,968,378 common shares issued and outstanding as of December 12, 2025, as reported by the company. He has sole voting and dispositive power over all 400,000 shares and no shared power. The filer certifies the shares were acquired and are held without the purpose or effect of changing or influencing control of C3is Inc.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

C3is Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

Y18284169

(CUSIP Number)

01/09/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. Y18284169

1

Names of Reporting Persons

Athanasios Tsiakmakis

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

GREECE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 400,000.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 400,000.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

400,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

5.02 %

12

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: C3is Inc.
(b)	Address of issuer's principal executive offices: 331 Kifissias Avenue, Kifissia, Athens, Greece, 14561
Item 2.
(a)	Name of person filing: Athanasios Tsiakmakis
(b)	Address or principal business office or, if none, residence: The address of the principal business office of the Reporting Person is Dimokratias 17, Agioi Anargyroi, Athens.
(c)	Citizenship: Greece
(d)	Title of class of securities: Common Stock, par value $0.01 per share
(e)	CUSIP No.: Y18284169
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: The information required by Item 4(a) is set forth in Row 9 of the cover page and is incorporated herein by reference.
(b)	Percent of class: The information required by Item 4(b) is set forth in Row 11 of the cover page and is incorporated herein by reference. The information in Row 11 is calculated on the basis of 7,968,378 shares of Common Stock issued and outstanding as of December 12, 2025, as reported by the Issuer in Post-Effective Amendment No. 5 to Form F-1 Registration Statement filed by the Issuer with the Securities and Exchange Commission on December 19, 2025.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: The information required by Item 4(c)(i) is set forth in Row 5 of the cover page and is incorporated herein by reference.
	(ii) Shared power to vote or to direct the vote: The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page and is incorporated herein by reference.
	(iii) Sole power to dispose or to direct the disposition of: The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page and is incorporated herein by reference.
	(iv) Shared power to dispose or to direct the disposition of: The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page and is incorporated herein by reference.
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Athanasios Tsiakmakis

Signature:	/s/ Athanasios Tsiakmakis
Name/Title:	Athanasios Tsiakmakis
Date:	01/13/2026

FAQ

What ownership stake in C3is Inc. (CISS) does Athanasios Tsiakmakis report?

Athanasios Tsiakmakis reports beneficial ownership of 400,000 shares of C3is Inc. common stock, representing 5.02% of the outstanding common shares.

How was the 5.02% ownership percentage in C3is Inc. calculated?

The 5.02% figure is based on 7,968,378 C3is Inc. common shares issued and outstanding as of December 12, 2025, as reported by the company in a post-effective amendment to its Form F-1.

Does Athanasios Tsiakmakis have sole or shared voting power over his C3is Inc. shares?

He reports sole voting power and sole dispositive power over all 400,000 C3is Inc. shares, with no shared voting or dispositive power.

Is the C3is Inc. stake held for the purpose of influencing control of the company?

No. He certifies that the securities were not acquired and are not held for the purpose or effect of changing or influencing the control of C3is Inc., consistent with a Schedule 13G passive ownership filing.

What type of securities does this Schedule 13G/A for C3is Inc. cover?

The filing covers common stock of C3is Inc., with a par value of $0.01 per share and CUSIP number Y18284169.

When was the reportable event for this C3is Inc. Schedule 13G/A?

The date of the event that triggered this amended Schedule 13G/A is reported as January 9, 2026.