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 January 2026

Commission File Number: 001-40155

Cosan S.A.

(Exact name of registrant as specified in its charter)

N/A

(Translation of registrant’s name into English)

Av. Brigadeiro Faria Lima, 4100, – 16th floor
São Paulo, SP 04538-132 Brazil
(Address of principal executive offices)

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

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COSAN S.A.

Publicly Held Company

CNPJ n° 50.746.577/0001-15

NIRE 35.300.177.045 | CVM Code 01983‑6

NOTICE TO THE MARKET

COSAN S.A. (B3: CSAN3; NYSE: CSAN) (“Cosan” or the “Company”) hereby informs its shareholders and the market in general that, in compliance with Article 12 of CVM Resolution No. 44/21, it received today a notice from Vertiz Holding S.A. (“Vertiz”) and from Fundo de Investimento em Participações BPAC3 – Multiestratégia Responsabilidade Limitada (“FIP BPAC3”), managed by BTG Pactual Serviços Financeiros S/A DTVM, informing the following:

1.	In accordance with the provisions of the Company’s Shareholders’ Agreement executed on November 7, 2025, and available on the Company’s and CVM’s websites, the BTG Vehicles and the Perfin Vehicle have detached a portion of their shareholding in Vertiz, and now also hold a direct stake in the Company.;

2.	Vertiz has reduced its stake in the Company from 1,450,000,000 common shares (equivalent to 36.56% of the Company’s total share capital) to 959,661,363 common shares (equivalent to 24.19% of the Company’s total share capital).;

3.	FIP BPAC3 has reached a position of approximately 331,513,280 common shares of the Company, equivalent to approximately 8.36% of the Company’s total share capital.

4.	The shareholders’ block maintains the same direct and indirect stake in the Company, and the bound and unbound shares will continue to vote in the same manner.

The full notices are attached to this announcement.

São Paulo, January 30, 2026

Rafael Bergman
Chief Financial and Investor Relations Officer

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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: January 30, 2026

	COSAN S.A.
	By:	/s/ Rafael Bergman
		Name: Rafael Bergman
		Title: Chief Financial Officer

Cosan S.A. 6-K