SABESP confirms EMAE share swap at 1.3195-for-1

Companhia de Saneamento Básico do Estado de São Paulo (SABESP) confirmed the timetable for its merger of shares issued by EMAE – Empresa Metropolitana de Águas e Energia S.A.

Rhea-AI Filing Summary

Companhia de Saneamento Básico do Estado de São Paulo (SABESP) confirmed the timetable for its merger of shares issued by EMAE – Empresa Metropolitana de Águas e Energia S.A. October 23, 2026, is the last trading day for EMAE shares on B3. EMAE shareholders holding shares on October 27, 2026, will receive 1.31950000000 SABESP common shares for each EMAE common or preferred share.

No shareholders exercised the withdrawal right, so no reimbursement will be paid. Fractional SABESP shares resulting from the merger will be grouped into whole shares and sold on B3’s spot market after consummation. For non-resident investors, SABESP is responsible for withholding income tax on any capital gain; a 25% rate applies if an investor does not provide their tax residence or confirm their classification within the applicable deadline. SABESP may deduct an amount equivalent to tax withheld from the SABESP shares otherwise due to that investor.

Filing Explained

In the share merger, SABESP will treat missing, inadequate, or late acquisition-cost documentation from a non-resident EMAE holder as a zero cost when calculating withholding on any capital gain, so no acquisition cost will reduce that tax base.

Key Figures

Exchange ratio: 1.31950000000 SABESP common shares per 1 EMAE common or preferred share Last EMAE trading day: October 23, 2026 SABESP share credit date: October 27, 2026 +2 more

5 metrics

Exchange ratio 1.31950000000 SABESP common shares per 1 EMAE common or preferred share Merger of shares

Last EMAE trading day October 23, 2026 Shares issued by EMAE on B3

SABESP share credit date October 27, 2026 For EMAE shareholders holding shares on that date

Withdrawal requests 0 requests Withdrawal-right period ended October 19, 2026

Withholding income tax rate 25% Applies to non-resident investors who do not provide tax residence or confirm classification within the applicable deadline

Key Terms

Withdrawal Right, Merger of Shares, Withholding Income Tax, fractional common shares

4 terms

Withdrawal Right regulatory

"period for the exercise of the Withdrawal Right"

Merger of Shares technical

"in the context of the merger by SABESP of the shares issued by EMAE"

Withholding Income Tax financial

"withholding the Withholding Income Tax ("WHT") on any capital gain"

fractional common shares technical

"Any fractional common shares issued by Sabesp resulting from the Merger"

A fractional common share is a portion of a single company share — less than one whole share — that gives you proportional ownership, dividends, and price movement tied to that company. Think of it like buying a slice of a pie instead of the whole pie; it lets investors use small amounts of money to diversify across more stocks and buy high-priced shares they couldn’t afford otherwise, though some broker rules may affect voting or settlement details.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What exchange ratio will EMAE shareholders receive in the SBS merger?

EMAE shareholders holding shares on October 27, 2026, will receive 1.31950000000 SABESP common shares for each EMAE common or preferred share under the merger of shares.

When will EMAE shares stop trading and SABESP shares be credited?

October 23, 2026, is the last trading day for EMAE shares on B3. The timetable sets October 27, 2026, for crediting SABESP shares to EMAE shareholders holding shares on that date.

How will SBS withhold tax for non-resident EMAE shareholders?

SABESP is responsible for withholding income tax on any capital gain of non-resident investors. If an investor does not provide their tax residence or confirm their classification by the applicable deadline, SABESP will apply a 25% rate. SABESP may deduct an amount equivalent to tax withheld from the SABESP shares otherwise due.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 10/21/2026 - 08:43 AM EDT Accepted by SEC EDGAR 10/21/2026 - 08:42 AM EDT Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 6-K

REPORT OF FOREIGN ISSUER
PURSUANT TO RULE 13a-16 OR 15d-16 OF THE

SECURITIES EXCHANGE ACT OF 1934

For October, 2026

(Commission File No. 1-31317)

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

(Exact name of registrant as specified in its charter)

Basic Sanitation Company of the State of Sao Paulo - SABESP

(Translation of Registrant's name into English)

Rua Costa Carvalho, 300
São Paulo, S.P., 05429-900
Federative Republic of Brazil

(Address of Registrant's principal executive offices)

Indicate by check mark whether the registrant files or will file
annual reports under cover Form 20-F or Form 40-F.

Form 20-F ___X___ 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)__.

Indicate by check mark whether the registrant by furnishing the
information contained in this Form is also thereby furnishing the
information to the Commission pursuant to Rule 12g3-2(b) under
the Securities Exchange Act of 1934.

Yes ______ No ___X___

If "Yes" is marked, indicated below the file number assigned to the
registrant in connection with Rule 12g3-2(b):

  COMPANHIA DE SANEAMENTO BÁSICO DO ESTADO DE SÃO PAULO – SABESP Publicly Held Company CNPJ/MF No. 43.776.517/0001-80 EMPRESA METROPOLITANA DE ÁGUAS E ENERGIA S.A. - EMAE Publicly Held Company CNPJ/MF No. 02.302.101/0001-42

JOINT MATERIAL FACT

RESULT OF THE EXERCISE OF THE WITHDRAWAL RIGHT AND CONFIRMATION OF THE TIMETABLE OF THE MERGER OF SHARES

Companhia de Saneamento Básico do Estado de São Paulo – SABESP ("SABESP") and EMAE – Empresa Metropolitana de Águas e Energia S.A. ("EMAE" and, together with SABESP, the "Companies"), pursuant to Article 157, Paragraph 4, of Law No. 6,404, dated December 15, 1976 ("Brazilian Corporations Law") and the provisions of CVM Resolution No. 44, dated August 23, 2021, as amended, further to the Joint Material Facts disclosed on April 24 and June 29, 2026 by the Companies; the Joint Notice to the Market disclosed on July 27, 2026 by the Companies; EMAE's Material Fact dated July 29, 2026; the Material Fact disclosed by Sabesp on July 30, 2026; and the Joint Material Facts disclosed by the Companies on September 16 and October 8, 2026, in the context of the merger by SABESP of the shares issued by EMAE ("Merger of Shares"), hereby present to their shareholders and the market in general the following information.

I. End of the Period and Result of the Exercise of the Withdrawal Right.

On October 19, 2026, the period for the exercise of the withdrawal right ("Withdrawal Right") by the shareholders dissenting from the resolution taken at EMAE's Extraordinary Shareholders' Meeting held on September 16, 2026, which approved the Merger of Shares, came to an end.

Given that EMAE did not receive any request for the exercise of the Withdrawal Right, the Companies clarify that there will be no amount to be paid as reimbursement to shareholders. Accordingly, the Companies clarify that the prerogative set forth in Article 137, Paragraph 3, of the Brazilian Corporations Law is not applicable.

II. Consummation of the Merger of Shares.

Pursuant to Exhibit I to this Material Fact, October 23, 2026 will be the last trading day for shares issued by EMAE on B3 S.A. – Brasil, Bolsa, Balcão ("B3") and, on October 27, 2026, EMAE shareholders holding shares on such date will receive shares issued by SABESP, in accordance with the exchange ratio of 1.31950000000 common shares issued by SABESP for each 1 (one) common or preferred share issued by EMAE, traded under the ticker SBSP3.

EMAE - Empresa Metropolitana de Águas e Energia S.A.

Av. Jornalista Roberto Marinho, 85, 16º andar, Cidade Monções | CEP 04576-010 | São Paulo – SP

Fone: (11) 2763-6504 | ri.emae.com.br

III. Fractional Shares.

Any fractional common shares issued by Sabesp resulting from the Merger of Shares will be grouped into whole numbers and subsequently sold on the spot market operated by B3 after the consummation of the Merger of Shares, pursuant to a notice to be duly disclosed to the market by SABESP, as applicable.

IV. Tax Treatment in the Merger of Shares.

As informed by the Companies in the Joint Material Fact disclosed on September 16, 2026, current EMAE shareholders may be subject to the payment of income tax on any capital gain in connection with the Merger of Shares, in addition to other taxes, in accordance with the legal and regulatory rules applicable to each category of investor. Any tax impacts arising from the Merger of Shares, including Income Tax on capital gains of EMAE shareholders, whether resident or non-resident in Brazil, shall be the sole responsibility of the respective shareholders, subject to applicable tax legislation.

Shareholders Resident in Brazil. EMAE shareholders resident in Brazil shall be responsible for any payment of the taxes applicable to them, and should consult their own advisors regarding the applicable tax treatment.

Shareholders Non-Resident in Brazil. Sabesp, in its capacity as the acquirer of the shares issued by EMAE, is responsible for withholding the Withholding Income Tax ("WHT") on any capital gain calculated in connection with the Merger of Shares of investors who are non-tax residents in Brazil ("NRI"), pursuant to applicable tax legislation.

The tax base for the WHT shall be the capital gain of the respective NRI, corresponding to the positive difference, if any, between (i) the per-share value of EMAE attributed in the exchange ratio under the Merger of Shares; and (ii) the acquisition cost of the shares issued by EMAE held by each NRI. Sabesp shall use the information provided by the NRI (directly or through their custody agents) for the calculation of the capital gain, and the NRI shall be responsible for the accuracy and completeness of such information and documents.

Sabesp: (i) shall consider the acquisition cost to be zero for NRI that fail to submit the acquisition cost of the shares issued by EMAE, or that submit the information and/or supporting documentation in an inadequate, insufficient, or untimely manner; and (ii) shall apply the rate of 25% on the capital gains of NRI that, within the same deadline, fail to inform their country or dependency of tax residence or domicile, or fail to confirm their classification under CMN/CVM Joint Resolution No. 13, in accordance with applicable legislation and regulations.

EMAE - Empresa Metropolitana de Águas e Energia S.A.

Av. Jornalista Roberto Marinho, 85, 16º andar, Cidade Monções | CEP 04576-010 | São Paulo – SP

Fone: (11) 2763-6504 | ri.emae.com.br

Sabesp may charge or offset the amount of WHT eventually withheld on behalf of the NRI by deducting from the number of SABESP shares that would be delivered to the shareholder an amount equivalent to that due for payment of the tax.

São Paulo, October 20, 2026

COMPANHIA DE SANEAMENTO BÁSICO DO ESTADO DE SÃO PAULO – SABESP     Daniel Szlak Chief Financial Officer and Investor Relations Officer EMAE – Empresa Metropolitana de Águas e Energia S.A.       Pedro Borges Petersen Chief Financial, Investor Relations and Administrative Officer  

EMAE - Empresa Metropolitana de Águas e Energia S.A.

Av. Jornalista Roberto Marinho, 85, 16º andar, Cidade Monções | CEP 04576-010 | São Paulo – SP

Fone: (11) 2763-6504 | ri.emae.com.br

EXHIBIT I

TIMETABLE OF THE MERGER OF SHARES

Date	Event
July 30	Sabesp’s Shareholders’ Meeting held at 11:00 a.m.
	Disclosure through the ENET system: (i) the minutes of Sabesp’s Shareholders’ Meeting; and (ii) Sabesp’s Material Fact regarding the approval at the Shareholders’ Meeting.
September 14	Publication of the minutes of Sabesp’s Shareholders’ Meeting in the newspaper “Valor Econômico”.
September 16	EMAE’s Shareholders’ Meeting held at 11:00 a.m.
	Disclosure through the ENET system: (i) the minutes of EMAE’s Shareholders’ Meeting; and (ii) the joint Material Fact regarding: (a) the approval of the Merger of Shares of EMAE, including the estimated timetable of events of the Merger of Shares; (b) the commencement of the Withdrawal Right, including information on the migration of EMAE’s bookkeeping from BTG (“Former Bookkeeping Agent”) to Itaú (“New Bookkeeping Agent”); and (c) information on the procedure for tax payment by INRs.
	Disclosure of EMAE’s Notice to the Market regarding the change of bookkeeping agent.
September 17	Publication of the minutes of EMAE’s Shareholders’ Meeting in the newspaper “Folha de São Paulo”.
September 18	Beginning of the period for the exercise of the Withdrawal Right.
September 30	Last day on which the Former Bookkeeping Agent will provide services to EMAE (brokerage-firm blocking, payments, transfers of title, etc.).
October 1	Update of EMAE’s Registration Form.
	Commencement of bookkeeping services for EMAE’s shares by the New Bookkeeping Agent.
October 8	Disclosure of a joint Material Fact regarding the update of the timetable of the Merger of Shares.

EMAE - Empresa Metropolitana de Águas e Energia S.A.

Av. Jornalista Roberto Marinho, 85, 16º andar, Cidade Monções | CEP 04576-010 | São Paulo – SP

Fone: (11) 2763-6504 | ri.emae.com.br

October 19	End of the period for the exercise of the Withdrawal Right.
	End of the period for NRIs to provide information regarding payment of income tax relating to any capital gain in connection with the exercise of the Withdrawal Right.
	Confirmation by B3 and the New Bookkeeping Agent of the result of the exercise of the Withdrawal Right.
October 20	Deadline for Sabesp and EMAE to assess the tax payment by the NRIs, in connection with the exercise of the Withdrawal Right, and provide the relevant information to B3.
	Disclosure of a joint Material Fact regarding the end of the Withdrawal Right exercise period and confirmation of the timetable of the Merger of Shares.
October 23	Last trading day for shares issued by EMAE on B3.
	End of the period for NRIs to provide information regarding payment of income tax relating to any capital gain in connection with the Merger of Shares.
October 27	Disclosure of a Material Fact by Sabesp confirming the consummation of the Merger of Shares.
	Credit of the shares issued by Sabesp to EMAE shareholders.
	Deadline for Sabesp and EMAE to assess the tax payment by the NRIs, in connection with the Merger of Shares, and provide the relevant information to B3.
November 4	Confirmation by B3 and the New Bookkeeping Agent of any fractional shares resulting from the Merger of Shares.
To be defined, as applicable.	Auction of fractional shares on B3, as applicable.
To be defined, as applicable.	Availability of payment relating to any fractional shares, net of fees, to former EMAE shareholders, as applicable.

EMAE - Empresa Metropolitana de Águas e Energia S.A.

Av. Jornalista Roberto Marinho, 85, 16º andar, Cidade Monções | CEP 04576-010 | São Paulo – SP

Fone: (11) 2763-6504 | ri.emae.com.br

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, in the city São Paulo, Brazil.

Date: October 21, 2026

Companhia de Saneamento Básico do Estado de São Paulo - SABESP
By:	/s/  Daniel Szlak
	Name: Daniel Szlak Title: Chief Financial Officer and Investor Relations Officer

FORWARD-LOOKING STATEMENTS

This press release may contain forward-looking statements. These statements are statements that are not historical facts, and are based on management's current view and estimates of future economic circumstances, industry conditions, company performance and financial results. The words "anticipates", "believes", "estimates", "expects", "plans" and similar expressions, as they relate to the company, are intended to identify forward-looking statements. Statements regarding the declaration or payment of dividends, the implementation of principal operating and financing strategies and capital expenditure plans, the direction of future operations and the factors or trends affecting financial condition, liquidity or results of operations are examples of forward-looking statements. Such statements reflect the current views of management and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, and operating factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations.