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 ~~June~~July 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

Graphics

COSAN S.A.

CNPJ nº 50.746.577/0001-15

NIRE 35.300.177.045

Publicly held company

CVM Code 19836

MATERIAL FACT

COSAN S.A. (B3: CSAN3; NYSE: CSAN) (“"Cosan”" or “the "Company”"), in compliance with ~~the provisions of~~ CVM Resolution No. 44 and further to the Material Fact disclosed on June 17, 2026, hereby informs its shareholders and the market in general that, ~~Radar~~following ~~Group,~~the onconcurrent exercise of the ~~date~~right of ~~yesterday,~~first ~~through~~refusal ~~certain~~by the lessees of ~~its~~the ~~subsidiaries~~land assets located in the State of Mato Grosso (~~“Radar”~~the "Properties"), ~~which~~the ~~hold~~parties ~~agricultural~~have ~~properties~~executed, ~~with~~on ~~investments~~this bydate, ~~Cosan~~an agreement for the consensual segregation of the Properties, ~~has~~as ~~entered~~well ~~into~~as anew purchase and sale ~~commitment~~agreements ~~agreement~~with ~~(“Purchase~~SLC Agrícola, Bom Futuro and ~~Sale~~Alexandre ~~Agreement”~~Jacques Bottan (the "Purchasing Lessees"), ~~for~~under the ~~disposal~~same commercial terms previously agreed upon (total transaction value of ~~part~~R$1.85 billion, of ~~the~~which ~~properties~~approximately inR$586 ~~its~~million ~~portfolio~~corresponds ~~(“Properties”~~to Cosan's indirect interest).

The ~~Properties~~closing ~~correspond to 12%~~ of ~~Radar’s total agricultural land portfolio, are in~~ the ~~state~~transaction ofremains ~~Mato~~subject ~~Grosso,~~to ~~comprise~~customary aconditions ~~total~~precedent ~~area of 41,214 hectares, and are used~~ for ~~the~~transactions ~~cultivation~~ of ~~soybeans,~~this ~~corn,~~nature and ~~cotton.~~is ~~The~~expected ~~total~~to ~~price~~occur ~~offered~~ by ~~the~~October ~~third-party buyer for these Properties is BRL 1.85 billion~~30, ~~of which approximately BRL 586 million corresponds to Cosan’s interest~~2026.

~~The~~Cosan ~~completion~~will ofkeep ~~the~~its ~~transaction~~shareholders isand ~~subject~~the tomarket ~~certain~~in ~~customary~~general ~~conditions~~duly ~~precedent~~informed ~~for~~in ~~this~~accordance ~~type~~with ofthe ~~transaction~~applicable regulations.

~~This~~São ~~transaction~~Paulo, isJuly ~~aligned with Cosan’s strategy of divestments~~9, ~~deleveraging, and portfolio simplification.~~2026

Cosan will keep its shareholders and the market duly informed in accordance with the applicable regulations.

São Paulo, June 17, 2026

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: ~~June~~July 179, 2026

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

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