Cosan S.A. (NYSE: CSAN) executes Rumo share sale and total return swap

Rhea-AI Filing Summary

Cosan S.A. reported that on December 15 it sold common shares of its subsidiary Rumo S.A. equal to approximately 4.98% of Rumo’s total share capital. At the same time, Cosan entered into total return swap derivative instruments that provide the same economic exposure as the shares sold.

The company explains that this financial transaction is part of its strategy focused on liquidity and cash management and states that it does not reduce Cosan’s political and economic rights in Rumo. Cosan also sent a communication to Rumo in line with Article 12 of CVM Resolution No. 44.

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: 001-40155

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 X Form 40-F

COSAN S.A.

CNPJ/MF n° 50.746.577/0001-15

NIRE 35.300.177.045

Public Company

CVM 19836

MATERIAL FACT

COSAN S.A. (B3: CSAN3; NYSE: CSAN) (“Cosan” or “Company”), in compliance with CVM Resolution No. 44, dated August 23, 2021, hereby informs its shareholders and the market in general that, on December 15, it carried out a transaction consisting of:
(i) the sale of common shares issued by its subsidiary, Rumo S.A. (“Rumo”), equivalent to approximately 4.98% of Rumo’s total share capital (“Shares”); and simultaneously
(ii) the execution of derivative instruments (total return swap), which represents the same economic exposure corresponding to the Shares mentioned in the previous item (“Financial Transaction”).

The Financial Transaction is part of the Company’s strategy focused on liquidity and cash management and does not reduce Cosan’s political and economic rights regarding Rumo.

The Company also informs that, on this date, it sent a communication to Rumo in accordance with Article 12 of CVM Resolution No. 44.

São Paulo, December 15, 2025.

Rafael Bergman

Chief Financial and Investor Relations Officer

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 15, 2025

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

FAQ

What transaction did Cosan S.A. (CSAN) disclose involving Rumo S.A.?

Cosan S.A. disclosed that it sold common shares issued by its subsidiary Rumo S.A. and, simultaneously, executed total return swap derivative instruments related to those shares.

How much of Rumo S.A.'s share capital did Cosan sell?

Cosan sold common shares of Rumo S.A. equivalent to approximately 4.98% of Rumo’s total share capital.

Why did Cosan carry out the Rumo share sale and total return swap?

Cosan states that the financial transaction is part of its strategy focused on liquidity and cash management.

Does the transaction affect Cosan's political or economic rights in Rumo?

Cosan states that the transaction does not reduce its political and economic rights regarding Rumo.

When did Cosan execute the Rumo share sale and derivative transaction?

Cosan carried out the sale of Rumo shares and the related total return swap on December 15, 2025.

Which regulation did Cosan reference in connection with this material fact?

Cosan referenced CVM Resolution No. 44, noting that it also sent a communication to Rumo under Article 12 of that resolution.