SCHEDULE 13G 0001896206 XXXXXXXX LIVE Common Stock, par value $0.01 per share 02/27/2026 0001951067 C3is Inc. Y18284177 331 KIFISSIAS AVENUE ERITHREA ATHENS J3 14561 Rule 13d-1(c) Alta Partners LLC NY 56176.00 0.00 56176.00 0.00 56176.00 5.2 OO C3is Inc. 331 KIFISSIAS AVENUE, ERITHREA, ATHENS, GREECE, 14561 Alta Partners LLC 1205 Franklin Avenue Garden City, New York 11530 New York Limited Liability Company Y 56,176 shares, representing shares issuable upon exercise of warrants. 5.2% 56,176 shares 0 shares 56,176 shares 0 shares Y N Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and 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. 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. Alta Partners LLC /s/ Steven Cohen 02/27/2026