<SEC-DOCUMENT>0001193125-25-327054.txt : 20251219
<SEC-HEADER>0001193125-25-327054.hdr.sgml : 20251219
<ACCEPTANCE-DATETIME>20251219170659
ACCESSION NUMBER:		0001193125-25-327054
CONFORMED SUBMISSION TYPE:	424B3
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20251219
DATE AS OF CHANGE:		20251219

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			C3is Inc.
		CENTRAL INDEX KEY:			0001951067
		STANDARD INDUSTRIAL CLASSIFICATION:	DEEP SEA FOREIGN TRANSPORTATION OF FREIGHT [4412]
		ORGANIZATION NAME:           	01 Energy & Transportation
		EIN:				000000000
		STATE OF INCORPORATION:			1T
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		424B3
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	333-272939
		FILM NUMBER:		251588449

	BUSINESS ADDRESS:	
		STREET 1:		331 KIFISSIAS AVENUE
		STREET 2:		ERITHREA
		CITY:			ATHENS
		STATE:			J3
		ZIP:			14561
		BUSINESS PHONE:		011-30-210-625-0001

	MAIL ADDRESS:	
		STREET 1:		331 KIFISSIAS AVENUE
		STREET 2:		ERITHREA
		CITY:			ATHENS
		STATE:			J3
		ZIP:			14561
</SEC-HEADER>
<DOCUMENT>
<TYPE>424B3
<SEQUENCE>1
<FILENAME>d87090d424b3.htm
<DESCRIPTION>424B3
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<TITLE>424B3</TITLE>
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<Center><DIV STYLE="width:8.5in" align="left">
 <P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="right"><B>Filed Pursuant to Rule 424(b)(3) </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="right"><B><FONT STYLE="white-space:nowrap">Registration&nbsp;No.&nbsp;333-272939</FONT> </B></P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"><B>PROSPECTUS SUPPLEMENT NO. 1 </B></P> <P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"><B>(TO PROSPECTUS DATED
DECEMBER&nbsp;18, 2025) </B></P> <P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:24pt; font-family:Times New Roman" ALIGN="center"><B>C3IS INC. </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; text-indent:4%; font-size:10pt; font-family:Times New Roman">This is a supplement (&#8220;Prospectus Supplement&#8221;) to the prospectus, dated December&nbsp;18, 2025 (&#8220;Prospectus&#8221;), of C3is
Inc. (the &#8220;Company&#8221;), which forms a part of the Company&#8217;s Registration Statement
<FONT STYLE="white-space:nowrap"><FONT STYLE="white-space:nowrap">on&nbsp;Form&nbsp;F-1&nbsp;(Registration&nbsp;No.&nbsp;333-272939),&nbsp;as</FONT></FONT> amended or supplemented from time to time. This Prospectus Supplement is being filed to
update and supplement the information included in the Prospectus with the information contained in our Report <FONT STYLE="white-space:nowrap">on&nbsp;Form&nbsp;6-K,&nbsp;furnished</FONT> to the U.S. Securities and Exchange Commission on
December&nbsp;19, 2025 <FONT STYLE="white-space:nowrap">(the&nbsp;&#8220;Form&nbsp;6-K&#8221;).&nbsp;Accordingly,</FONT> we have attached <FONT STYLE="white-space:nowrap">the&nbsp;Form&nbsp;6-K&nbsp;to</FONT> this Prospectus Supplement. </P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; text-indent:4%; font-size:10pt; font-family:Times New Roman">This Prospectus Supplement should be read in conjunction with, and delivered with, the Prospectus and is qualified by reference to the
Prospectus except to the extent that the information in this Prospectus Supplement supersedes the information contained in the Prospectus. This Prospectus Supplement is not complete without, and may not be delivered or utilized except in connection
with, the Prospectus, including any amendments or supplements to it. </P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; text-indent:4%; font-size:12pt; font-family:Times New Roman"><B>Investing in our securities involves a high degree of risk. See &#8220;<U>Risk Factors</U>&#8221; beginning on page 8 of the Prospectus for
a discussion of information that should be considered in connection with an investment in our securities. </B></P> <P STYLE="margin-top:12pt; margin-bottom:0pt; text-indent:4%; font-size:10pt; font-family:Times New Roman"><B>Neither the Securities
and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>The date of this prospectus supplement is December&nbsp;19, 2025. </B></P>
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<DIV STYLE="line-height:1.0pt;margin-top:0pt;margin-bottom:0pt;border-bottom:1px solid #000000">&nbsp;
</DIV><DIV STYLE="line-height:3.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1px solid #000000">&nbsp;</DIV> <P STYLE="margin-top:4pt; margin-bottom:0pt; font-size:18pt; font-family:Times New Roman" ALIGN="center"><B>UNITED STATES </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:18pt; font-family:Times New Roman" ALIGN="center"><B>SECURITIES AND EXCHANGE COMMISSION </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:12pt; font-family:Times New Roman" ALIGN="center"><B>Washington, D.C. 20549 </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:18pt; font-family:Times New Roman" ALIGN="center"><B><FONT STYLE="white-space:nowrap">FORM&nbsp;6-K</FONT> </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:12pt; font-family:Times New Roman" ALIGN="center"><B>REPORT OF FOREIGN PRIVATE ISSUER </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:12pt; font-family:Times New Roman" ALIGN="center"><B>PURSUANT TO <FONT STYLE="white-space:nowrap"><FONT STYLE="white-space:nowrap">RULE&nbsp;13a-16&nbsp;OR&nbsp;15d-16</FONT></FONT> </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:12pt; font-family:Times New Roman" ALIGN="center"><B>UNDER THE SECURITIES EXCHANGE ACT OF 1934 </B></P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>For the month of December 2025 </B></P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>Commission File <FONT STYLE="white-space:nowrap">Number&nbsp;001-41717</FONT> </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:24pt; font-family:Times New Roman" ALIGN="center"><B>C3IS INC. </B></P> <P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>(Translation
of registrant&#8217;s name into English) </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>331 Kifissias Avenue, Kifissia 14561 Athens, Greece </B></P>
<P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:8pt; font-family:Times New Roman" ALIGN="center"><B>(Address of principal executive office) </B></P>
<P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><center><DIV STYLE="line-height:6.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1.00pt solid #000000;width:21%">&nbsp;</DIV></center>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">Indicate by check mark whether the registrant files or will file annual reports under cover of <FONT STYLE="white-space:nowrap">Form&nbsp;20-F&nbsp;or</FONT> <FONT
STYLE="white-space:nowrap">Form&nbsp;40-F.</FONT> </P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><FONT STYLE="white-space:nowrap"><FONT STYLE="white-space:nowrap">Form&nbsp;20-F&#8194;&#9746;&#8195;&#8195;&#8195;Form&nbsp;
40-F&#8194;&#9744;</FONT></FONT> </P>
<P STYLE="font-size:10pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P><DIV STYLE="line-height:1.0pt;margin-top:0pt;margin-bottom:0pt;border-bottom:1px solid #000000">&nbsp;
</DIV><DIV STYLE="line-height:3.0pt;margin-top:0pt;margin-bottom:2pt;border-bottom:1px solid #000000">&nbsp;</DIV>
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<Center><DIV STYLE="width:8.5in" align="left">
 <P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>INFORMATION CONTAINED IN THIS
<FONT STYLE="white-space:nowrap">FORM&nbsp;6-K&nbsp;REPORT</FONT> </B></P> <P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"><B>Vessel Acquisition Agreement </B></P>
<P STYLE="margin-top:6pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">C3is Inc. (the &#8220;Company&#8221;) has entered into an agreement to acquire a South Korean-built, in 2008, product tanker with 50,000 dwt capacity for a
purchase price of $16.88&nbsp;million, from an entity affiliated with Brave Maritime Corp Inc. The transaction with Brave Maritime, which is affiliated with members of the Vafias family, was approved by the independent directors of the Company,
which obtained independent valuations of the vessel and based the purchase price on the average of these valuations. </P> <P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">The vessel is expected to be
delivered in the second or third quarter of 2026. The Company has the option to pay for the vessel one year after the date of the purchase agreement, without interest. </P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">Following this vessel delivery, and assuming no further acquisitions or dispositions, the Company&#8217;s fleet will total 5 vessels, three Handysize drybulk
carriers with a total capacity of 97,664 deadweight tons (dwt), an Aframax oil tanker with a capacity of approximately 115,800 dwt and a product tanker with a capacity of approximately 50,000 dwt, resulting in a fleet total capacity of approximately
263,464 dwt. </P> <P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center">***** </P> <P STYLE="margin-top:6pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">This report on <FONT
STYLE="white-space:nowrap">Form&nbsp;6-K</FONT> is hereby incorporated by reference into the Company&#8217;s Registration Statement on <FONT STYLE="white-space:nowrap">Form&nbsp;S-8</FONT>
<FONT STYLE="white-space:nowrap">(Reg.&nbsp;No.&nbsp;333-273306)</FONT> filed with the Securities and Exchange Commission on July&nbsp;18, 2023 and Registration Statement on <FONT STYLE="white-space:nowrap">Form&nbsp;F-3</FONT> <FONT
STYLE="white-space:nowrap">(Reg.&nbsp;No.&nbsp;333-&nbsp;285135)</FONT> filed with the Securities and Exchange Commission on February&nbsp;21, 2025. </P>
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 <P STYLE="margin-top:0pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman" ALIGN="center"><B>SIGNATURES </B></P>
<P STYLE="margin-top:12pt; margin-bottom:0pt; text-indent:4%; font-size:10pt; font-family:Times New Roman">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. </P> <P STYLE="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman">Date: December&nbsp;19, 2025 </P> <P STYLE="font-size:12pt;margin-top:0pt;margin-bottom:0pt">&nbsp;</P>
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<TD VALIGN="top" COLSPAN="3"> <P STYLE=" margin-top:0pt ; margin-bottom:0pt; margin-left:1.00em; text-indent:-1.00em; font-size:10pt; font-family:Times New Roman"><B>C3IS INC.</B></P></TD></TR>
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<TD VALIGN="top">By:</TD>
<TD VALIGN="bottom" STYLE=" BORDER-BOTTOM:1px solid #000000;">&nbsp;</TD>
<TD VALIGN="top" STYLE="BORDER-BOTTOM:1px solid #000000;">/s/ Nina Pyndiah</TD></TR>
<TR STYLE="page-break-inside:avoid ; font-family:Times New Roman; font-size:10pt">
<TD VALIGN="bottom">Name:</TD>
<TD VALIGN="bottom">&nbsp;</TD>
<TD VALIGN="bottom">Nina Pyndiah</TD></TR>
<TR STYLE="page-break-inside:avoid ; font-family:Times New Roman; font-size:10pt">
<TD VALIGN="bottom">Title:</TD>
<TD VALIGN="bottom">&nbsp;</TD>
<TD VALIGN="bottom">Chief Financial Officer</TD></TR>
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