Cosan (NYSE: CSAN) sells 4.96% Rumo stake, maintains exposure with swaps

Rhea-AI Filing Summary

Cosan S.A. reports that on December 22, 2025 it sold common shares of its subsidiary Rumo S.A. equivalent to approximately 4.96% of Rumo’s total share capital and, at the same time, entered into total return swap derivative instruments that provide the same economic exposure to those shares. This structure is described as part of Cosan’s strategy focused on liquidity and cash management.

Cosan states that the move does not reduce its political and economic rights in Rumo. After the transaction, Cosan’s overall participation in Rumo’s total share capital remains unchanged, with a 20.33% direct stake and a further 9.94% held via derivative instruments.

Insights

Equity & Derivatives Structure Analyst

Cosan monetizes Rumo shares for liquidity while keeping its economic and governance exposure.

Cosan sold Rumo S.A. common shares equal to about 4.96% of Rumo’s total share capital and simultaneously executed total return swaps on the same exposure. This means it converts a direct equity position into a derivative-based position while preserving similar economic outcomes linked to Rumo’s performance.

The company explicitly frames this as part of a strategy focused on liquidity and cash management, suggesting a desire to optimize cash resources without changing its stance toward the asset. It also states that its political and economic rights regarding Rumo are not reduced, which is important for understanding that its influence and value linkage to Rumo continue.

After these steps, Cosan’s participation in Rumo’s total share capital is described as unchanged, at 20.33% held directly and 9.94% via derivatives instruments. Future disclosures in company communications and reports may provide more detail on how this structure affects interest costs, cash balances, or risk management over time.

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 22, 2025, it carried out a transaction consisting of:
(i) the sale of common shares issued by its subsidiary, Rumo S.A. (“Rumo”), equivalent to approximately 4.96% 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.

Company’s total participation in Rumo’s total share capital remains unchanged, compounded by 20.33% direct stake and 9.94% via derivatives instruments.

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 22, 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 22, 2025

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

FAQ

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

Cosan S.A. announced that on December 22, 2025 it sold common shares of its subsidiary Rumo S.A. equivalent to approximately 4.96% of Rumo’s total share capital and simultaneously entered into total return swap derivative instruments referencing the same economic exposure.

Why did Cosan S.A. (CSAN) carry out the sale of Rumo S.A. shares and derivatives?

Cosan stated that the combination of selling Rumo shares and executing total return swaps is part of its strategy focused on liquidity and cash management, while preserving its economic exposure to Rumo.

Did Cosan S.A. change its total participation in Rumo S.A. with this transaction?

Cosan stated that its total participation in Rumo’s total share capital remains unchanged after the transaction, consisting of a 20.33% direct stake and 9.94% via derivative instruments.

How does the transaction affect Cosan S.A.’s political and economic rights in Rumo S.A.?

Cosan explained that the financial transaction does not reduce its political and economic rights regarding Rumo, indicating that its governance influence and economic linkage to Rumo remain intact.

What type of derivative did Cosan S.A. use in connection with the Rumo S.A. shares?

Cosan used total return swap derivative instruments, which it describes as providing the same economic exposure as the sold shares of Rumo S.A.

Did Cosan S.A. notify Rumo S.A. about this share and derivative transaction?

Cosan stated that it sent a communication to Rumo S.A. on the same date in accordance with Article 12 of CVM Resolution No. 44.