C3is Inc. (CISS) details $9M unit sale with resettable and pre-funded warrants

Rhea-AI Filing Summary

C3is Inc. completed a registered sale of 7,500,000 units, raising about $9.0 million in gross proceeds before fees and expenses.

The transaction included 1,700,000 common units, each with one common share plus Class D and Class E warrants, and 5,800,000 pre‑funded units that replace the share with a pre‑funded warrant exercisable at $0.00001 per share. Class D warrants are immediately exercisable at an initial price of $1.20, then automatically reset after a 10‑trading‑day period to an Adjustment Price tied to a floor of $0.344 based on the Nasdaq Minimum Price and the lowest volume‑weighted average prices, with proportional increases in underlying shares to keep aggregate exercise value unchanged. Class E warrants are immediately exercisable at $0.00001 per share with no expiration and initially no underlying shares, but after the adjustment period they provide additional shares so each holder’s total shares reflect the unit purchase price divided by the final Adjustment Price, minus shares already received.

Insights

Capital markets and securities structure analyst

C3is raises $9M through a highly structured unit deal with resettable warrants.

C3is Inc. has completed a registered sale of 7,500,000 units for about $9.0 million in gross proceeds. The mix of 1,700,000 common units and 5,800,000 pre‑funded units combines immediate equity, very low‑priced pre‑funded warrants, and two new warrant classes issued together.

The Class D warrants start with a $1.20 exercise price but automatically reset after a 10‑trading‑day Adjustment Period to an Adjustment Price linked to a floor of $0.344 and the lowest daily VWAPs. When this reset occurs, the number of underlying shares increases so that the total exercise value across the warrants stays the same. Ongoing six‑month adjustment mechanics then further tie the exercise price to future Nasdaq Minimum Prices and VWAPs.

The Class E warrants are immediately exercisable at $0.00001 per share with no expiration and initially no underlying shares. After the Adjustment Period, the number of shares per Class E warrant is set so that, on full exercise, each holder’s total shares reflect the unit purchase price divided by the final Adjustment Price, less shares already issued in the units. This structure can lead to a variable and potentially large number of future shares, and the actual impact depends on future trading prices and holder exercise decisions.

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 December 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

On December 12, 2025, C3is Inc. (the “Company”) completed a registered offering (the “Offering”) of 7,500,000 units, consisting of (a) 1,700,000 common units (“Common Units”), each Common Unit consisting of one common share, par value $0.01 per share, of the Company (“Common Share”), one Class D Warrant to purchase one Common Share or otherwise such greater number of Common Shares, up to 26,162,790, as determined under the automatic adjustment feature of the Class D Warrant (“Class D Warrant”), and one Class E Warrant exercisable for that number of Common Shares, up to 18,662,790, determined in accordance with the adjustment formula of the Class E Warrant (“Class E Warrant”), and (b) 5,800,000 pre-funded units (“Pre-Funded Units”), each Pre-Funded Unit consisting of one pre-funded warrant to purchase one Common Share at an exercise price of $0.00001 per Common Share, one Class D Warrant and one Class E Warrant.

The aggregate gross proceeds to the Company from the Offering, before deducting placement agent fees and other expenses payable by the Company, were approximately $9.0 million.

Attached to this report on Form 6-K as Exhibit 1.1 is a copy of the Placement Agent Agreement, dated December 11, 2025, by and between the Company and Aegis Capital Corp.

Attached to this report on Form 6-K as Exhibit 4.1 is a copy of the form of Class D Warrant.

Attached to this report on Form 6-K as Exhibit 4.2 is a copy of the form of Class E Warrant.

Attached to this report on Form 6-K as Exhibit 4.3 is a copy of the form of Pre-funded Warrant.

Each Class D Warrant is exercisable upon issuance and expires five years after the issuance date. The initial exercise price of the Class D Warrants is $1.20. On the 10th trading day following the closing of this offering, the exercise price of the outstanding Class D Warrants will automatically reset to the “Adjustment Price,” which shall be the greater of (i) the Floor Price (as defined below) based on the Nasdaq Minimum Price (as defined in Nasdaq Listing Rule 5635(d)(1)(A), which is as the lower of the most recent Nasdaq Official Closing Price for the Common Shares and the average of the Nasdaq Official Closing Price of the Common Shares over the last five trading days) immediately preceding the pricing of this offering, which equals $0.344, or (ii) the lesser of (x) the then exercise price and (y) the lowest daily volume-weighted average price (“VWAP”) of the Common Shares during such 10 trading days period (the “Adjustment Period”), and the number of Common Shares underlying the then-outstanding Class D Warrants will be proportionally increased such that the then aggregate exercise price of all such Class D Warrants based on the Adjustment Price, equals the aggregate exercise price of all such Class D Warrants on the original issuance date that remain outstanding. The “Floor Price” equals 20% of the most recent Nasdaq Minimum Price of the Common Shares immediately prior to the applicable date of determination. Five trading days after the six-month anniversary of the closing of this offering and after every six-month anniversary thereof, the exercise price of the then-outstanding Class D Warrants will be automatically adjusted to equal the greater of (i) the Floor Price based on the Nasdaq Minimum Price as of the date of the applicable six-month anniversary or (ii) the lesser of (x) the then exercise price and (y) the lowest daily VWAP during such five-trading-day period, with the number of Common Shares underlying the then-outstanding Class D Warrants remaining unchanged.

Each Class E Warrant is immediately exercisable upon issuance at an exercise price of $0.00001 per share with no expiration. The number of Common Shares issuable upon the exercise of the Class E Warrants is initially zero. Following the Adjustment Period, the number of Common Shares underlying each Class E Warrant will be automatically increased so that each holder of Class E Warrants will, after the adjustment and upon full exercise of the Class E Warrant, receive a number of Common Shares equal to (A) the aggregate purchase price such holder paid for the units in this offering divided by the Adjustment Price minus (B) the number of Common Shares issued to such holder as part of the units purchased in this offering.

A detailed description of the Class D, Class E and Pre-funded Warrants is set forth under the heading “Description of Securities We Are Offering” in the Prospectus filed by the Company with the Securities and Exchange Commission pursuant to Rule 424(b)(4) on December 11, 2025, which is qualified by reference to the forms of such warrants which are filed as exhibits to this report.

****

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.

EXHIBIT INDEX

1.1		Placement Agent Agreement, dated December 11, 2025, by and between the Company and Aegis Capital Corp.
4.1		Form of Class D Warrant
4.2		Form of Class E Warrant
4.3		Form of Pre-funded Warrant

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: December 12, 2025

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

FAQ

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

C3is Inc. reported that it completed a registered offering of 7,500,000 units, consisting of common units and pre‑funded units, for aggregate gross proceeds of approximately $9.0 million.

How many units did C3is Inc. sell and what types were included?

The company sold 7,500,000 units in total, made up of 1,700,000 common units and 5,800,000 pre‑funded units. Each common unit includes one common share, one Class D warrant, and one Class E warrant. Each pre‑funded unit includes one pre‑funded warrant, one Class D warrant, and one Class E warrant.

How much capital did C3is Inc. (CISS) raise in this offering?

The offering generated aggregate gross proceeds of approximately $9.0 million for C3is Inc., before deducting placement agent fees and other expenses payable by the company.

What are the key terms of the C3is Class D warrants?

Each Class D warrant is exercisable upon issuance, has an initial exercise price of $1.20 per share, and expires five years after issuance. On the 10th trading day after closing, the exercise price resets to an Adjustment Price based on a floor of $0.344 tied to the Nasdaq Minimum Price and the lowest daily VWAP during the 10‑day period, with the number of underlying shares increased so the aggregate exercise price remains constant. Additional automatic adjustments occur every six months using similar formulas.

What are the main features of the C3is Class E warrants?

Each Class E warrant is immediately exercisable at an exercise price of $0.00001 per share and has no expiration. Initially, no shares are issuable, but after the 10‑trading‑day Adjustment Period, the number of shares per warrant is increased so that, on full exercise, a holder receives a number of common shares equal to the aggregate purchase price paid for the units divided by the Adjustment Price, minus the common shares already issued in the units.

What is a pre-funded unit and pre-funded warrant in the C3is offering?

Each pre‑funded unit includes one pre‑funded warrant instead of an immediate common share, plus one Class D and one Class E warrant. The pre‑funded warrant allows the holder to purchase one common share at a very low exercise price of $0.00001 per share.

How is this C3is 6-K related to other registration statements?

The report states that it is incorporated by reference into C3is Inc.’s Registration Statement on Form S‑8 (No. 333‑273306) and Registration Statement on Form F‑3 (No. 333‑285135), allowing the described information and exhibits to be used in those registrations.