6-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 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 September, 2025.

Commission File Number 001-38755

Suzano S.A. (Exact name of registrant as specified in its charter)

SUZANO INC. (Translation of Registrant’s Name into English)

Av. Professor Magalhaes Neto, 1,752 10th Floor, Rooms 1010 and 1011 Salvador, Brazil 41 810-012 (Address of principal executive office)

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 ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐

Enclosures:

Exhibit 99.1 – Notice to the Market - Early Redemption

SIGNATURE

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: September 19th, 2025

Document

NOTICE TO THE MARKET

SUZANO S.A.

Publicly Held Company with Authorized Capital

CNPJ/MF No. 16.404.287/0001-55

NIRE 29.3.0001633-1

São Paulo, September 19, 2025 – Suzano S.A. ("Suzano" or "Company") (B3: SUZB3 | NYSE: SUZ) hereby informs its shareholders and the market that will carry out, on September 26, 2025, the full optional early redemption of the simple, non-convertible, unsecured debentures of the 8th issuance, identified by the code SUZB18, issued by the Company (“Debentures”), originally maturing on September 15, 2028, pursuant to the Clause 7.14 of the Private Instrument of Public Issuance of Simple, Non-Convertible, Unsecured Debentures of the 8th Issuance of Suzano S.A. (Instrumento Particular de Escritura de Emissão Pública de Debêntures Simples, Não Conversíveis em Ações, da Espécie Quirografária, da 8ª(Oitava) Emissão de Suzano S.A.) entered into between the Company and Pentágono S.A. Distribuidora de Títulos e Valores Mobiliários, on September 13, 2019, as amended (“Indenture”).

The redemption will be carried out through the payment of the total remaining principal amount of R$750,000,000.00, corresponding to the outstanding nominal unit value of all Debentures, plus the Remuneration (as defined in the Indenture), calculated on a pro rata temporis basis from the First Subscription Date of the Debentures (as defined in the Indenture) or the date of the last Remuneration payment (as defined in the Indenture), as applicable, until the actual payment date, plus a premium applicable to the early redemption amount described above, calculated pursuant to Clause 7.14 of the Indenture. The redeemed Debentures will be cancelled.

This early redemption is aligned with the Company's active liability management strategy, aimed at optimizing its capital structure and reducing the cost of debt.

Suzano reiterates its commitment with transparency with its shareholders and investors.

São Paulo, September 19, 2025.

Marcos Moreno Chagas Assumpção

Executive Vice-President of Finance and Investor Relations