FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

For the month of February, 2026

Commission File Number: 001-12518

Banco Santander, S.A.

(Exact name of registrant as specified in its charter)

Ciudad Grupo Santander

28660 Boadilla del Monte (Madrid) Spain

(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

Banco Santander, S.A.

TABLE OF CONTENTS

Item

1	Report of Inside Information dated February 25, 2026

Item 1

Banco Santander, S.A. (“Banco Santander” or the “Bank”), in compliance with the Securities Market legislation, hereby communicates the following:

INSIDE INFORMATION

The board of directors of Banco Santander, S.A. has resolved to submit to the 2026 Annual Shareholders’ Meeting, in application of the Bank’s current shareholder remuneration policy, the approval of the payment against 2025 results of a final gross cash dividend of €12.50 cents per share entitled to receive dividends. Subject to the approval of the 2026 Annual Shareholders’ Meeting, the dividend would be payable from 5 May 2026. Thus, the last day to trade shares with a right to receive the dividend would be 29 April, the ex-dividend date would be 30 April and the record date would be 4 May.

The 2026 Annual Shareholders’ Meeting will be called today to be held on 26 March 2026, on first call, or on 27 March 2026, on second call, with the agenda below. The meeting is expected to be held on second call.

Agenda for the 2026 AGM

Annual accounts and corporate management.

1 A

Annual accounts and management reports of Banco Santander, S.A. and of its consolidated group for 2025.

1 B

Consolidated non-financial information statement for 2025, which forms part of the consolidated management report.

1 C

Corporate management during 2025.

Shareholder remuneration.

2 A

Allocation of 2025 results.

2 B

Share capital reduction by a maximum amount of 663,227,913 euros, through the cancellation of up to 1,326,455,826 own shares. Delegation of powers.

2 C

Share capital reduction by a maximum amount of 734,465,975 euros, through the cancellation of up to 1,468,931,950 own shares. Delegation of powers.

External auditor and independent verifier.

3 A

Re-election of the external auditor for financial year 2026.

3 B

Appointment of the sustainability information verifier for financial year 2026.

Board of directors: appointment and re-election of directors.

4 A

Setting of the number of directors.

4 B

Appointment of Ms Deborah Vieitas.

4 C

Re-election of Ms Sol Daurella.

4 D

Re-election of Ms Gina Díez Barroso.

4 E

Re-election of Mr Carlos Barrabés.

4 F

Re-election of Mr Antonio Weiss.

Remuneration.

5 A

Directors’ remuneration policy.

5 B

Approval of the maximum ratio between fixed and variable components of the total remuneration of executive directors and other employees belonging to categories whose professional activities have a significant impact on the risk profile.

5 C

Application of the Group’s buyout regulations.

5 D

Annual directors’ remuneration report (consultative vote).

Share capital and convertible securities.

6 A

Authorization to the board of directors to increase the Bank’s share capital on one or more occasions and at any time within a period of three years, through cash contributions and up to a maximum nominal amount of 3,672,329,875.50 euros. Authorization to exclude pre-emptive subscription rights.

6 B

Authorization to the board of directors to issue securities convertible into shares of Banco Santander within a period of five years and up to an aggregate maximum limit of 10,000 million euros. Setting of the criteria for determining the basis and methods of conversion. Authorization to increase share capital and to exclude pre-emptive subscription rights.

6 C

Increase in share capital by a nominal amount of 167,404,608 euros, by means of the issuance of 334,809,216 new shares, with in-kind contributions consisting of common shares of Webster Financial Corporation. Authorization to execute the capital increase and to determine the share premium, and possibility of incomplete subscription.

Authorization to the board and granting of powers for the formalization into public instrument.

Boadilla del Monte (Madrid), 25 February 2026

No Offer or Solicitation

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended (the “Securities Act”). No investment activity should be undertaken on the basis of the information contained in this communication. By making this communication available, no advice or recommendation is being given to buy, sell or otherwise deal in any securities or investments whatsoever.

Forward-looking Statements

This communication contains statements that constitute “forward-looking statements” within the meaning of, and subject to the protections of, Section 27A of the Securities Act, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, and the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. Forward-looking statements can be identified by words such as “achieve,” “anticipate,” “assume,” “believe,” “could,” “deliver,” “drive,” “enhance,” “estimate,” “expect,” “focus,” “future,” “goal,” “grow,” “guidance,” “intend,” “may,” “might,” “plan,” “position,” “potential,” “predict,” “project,” “opportunity,” “outlook,” “should,” “strategy,” “target,” “trajectory,” “trend,” “will,” “would,” and other similar words and expressions or the negative of such terms or other comparable terminology. Forward-looking statements include, but are not limited to, statements about business strategy, goals and objectives, projected financial and operating results, including outlook for future growth, and future share dividends, share repurchases and other uses of capital. These statements are not historical facts, but instead represent our beliefs regarding future events, many of which, by their nature, are inherently uncertain and outside of our control. As forward-looking statements involve significant risks and uncertainties, readers are cautioned not to place undue reliance on such statements.

Webster Financial Corporation’s (“Webster”) and Banco Santander S.A.’s (“Banco Santander”) actual results, financial condition and achievements may differ materially from those indicated in these forward-looking statements. Important factors that could cause Webster’s and Banco Santander’s actual results, financial condition and achievements to differ materially from those indicated in such forward-looking statements include, in addition to those set forth in Webster’s and Banco Santander’s filings with the U.S. Securities and Exchange Commission (the “SEC”): (1) the risk that the cost savings, synergies and other benefits from the acquisition of Webster by Banco Santander (the “Transaction”) may not be fully realized or may take longer than anticipated to be realized, including as a result of changes in, or problems arising from, general economic and market conditions, interest and exchange rates, monetary policy, laws and regulations and their enforcement, and the degree of competition in the geographic and business areas in which Webster and Banco Santander operate; (2) the failure of the closing conditions in the Transaction agreement by and among Webster, Banco Santander and a wholly owned subsidiary of Webster providing for the Transaction to be satisfied, or any unexpected delay in closing the Transaction or the occurrence of any event, change or other circumstances that could delay the Transaction or could give rise to the termination of the Transaction agreement; (3) the outcome of any legal or regulatory proceedings or governmental inquiries or investigations that may be currently pending or later instituted against Webster, Banco Santander or the combined company; (4) the possibility that the Transaction does not close when expected or at all because required regulatory, stockholder or other approvals and other conditions to closing are not received or satisfied on a timely basis or at all (and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the proposed Transaction); (5) disruption to the parties’ businesses as a result of the announcement and pendency of the Transaction; (6) the costs associated with the anticipated length of time of the pendency of the Transaction, including the restrictions contained in the definitive Transaction agreement on the ability of Webster to operate its business outside the ordinary course during the pendency of the Transaction; (7) risks related to management and oversight of the expanded business and operations of the combined company following the closing of the proposed Transaction; (8) the risk that the integration of Webster’s operations with Banco Santander’s will be materially delayed or will be more costly or difficult than expected or that the parties are otherwise unable to successfully integrate each party’s businesses into the other’s businesses; (9) the possibility that the Transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; (10) reputational risk and potential adverse reactions of Webster’s or Banco Santander’s customers, employees, vendors, contractors or other business partners, including those resulting from the announcement or completion of the Transaction; (11) the dilution caused by Banco Santander’s issuance of additional ordinary shares and corresponding American depositary shares, each representing the right to receive one of its ordinary shares (“ADSs”), in connection with the Transaction; (12) the possibility that any announcements relating to the Transaction could have adverse effects on the market price of Webster’s common stock and Banco Santander’s ordinary shares and ADSs; (13) a material adverse change in the condition of Webster or Banco Santander; (14) the extent to which Webster’s or Santander’s businesses perform consistent with management’s expectations; (15) Webster’s and Banco Santander’s ability to take advantage of growth opportunities and implement targeted initiatives in the timeframe and on the terms currently expected; (16) the inability to sustain revenue and earnings growth; (17) the execution and efficacy of recent strategic investments; (18) the impact of macroeconomic factors, such as changes in general economic conditions and monetary and fiscal policy, particularly on interest rates; (19) changes in customer behavior; (20) unfavorable developments concerning credit quality; (21) declines in the businesses or industries of Webster’s or

Banco Santander’s customers; (22) the possibility that the combined company is subject to additional regulatory requirements as a result of the proposed Transaction or expansion of the combined company’s business operations following the proposed Transaction; (23) general competitive, political and market conditions and other factors that may affect future returns of Webster and Banco Santander, including changes in asset quality and credit risk; (24) security risks, including cybersecurity and data privacy risks, and capital markets; (25) inflation; (26) the impact, extent and timing of technological changes; (27) capital management activities; (28) competitive product and pricing pressures; (29) the outcomes of legal and regulatory proceedings and related financial services industry matters; and (30) compliance with regulatory requirements. Any forward-looking statement made in this communication is based solely on information currently available to us and speaks only as of the date on which it is made.

Webster and Banco Santander undertake no obligation to publicly update any forward-looking statement, whether written or oral, that may be made from time to time, whether as a result of new information, future developments or otherwise, except to the extent required by law. These and other important factors, including those discussed under “Risk Factors” in Webster’s Annual Report on Form 10-K for the year ended December 31, 2024 (available at: https://www.sec.gov/ix?doc=/Archives/edgar/data/0000801337/000080133725000004/wbs-20241231.htm), and Banco Santander’s Annual Report on Form 20-F for the year ended December 31, 2024 (available at: https://www.sec.gov/ix?doc=/Archives/edgar/data/0000891478/000089147825000054/san-20241231.htm), as well as Webster’s and Banco Santander’s subsequent filings with the SEC, may cause actual results, performance or achievements to differ materially from those expressed or implied by these forward-looking statements. The forward-looking statements herein are made only as of the date they were first issued, and unless otherwise required by applicable securities laws, Webster and Banco Santander disclaim any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events, or otherwise.

ADDITIONAL INFORMATION ABOUT THE TRANSACTION AND WHERE TO FIND IT

INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT ON FORM F-4 AND THE PROXY STATEMENT/PROSPECTUS INCLUDED WITHIN THE REGISTRATION STATEMENT ON FORM F-4 WHEN THEY BECOME AVAILABLE, AS WELL AS ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC IN CONNECTION WITH THE TRANSACTION OR INCORPORATED BY REFERENCE INTO THE REGISTRATION STATEMENT ON FORM F-4 AND THE PROXY STATEMENT/PROSPECTUS, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION REGARDING WEBSTER, BANCO SANTANDER, THE TRANSACTION AND RELATED MATTERS.

Investors and security holders may obtain free copies of these documents and other documents filed with the SEC by Webster or Banco Santander through the website maintained by the SEC at http://www.sec.gov or by contacting the investor relations department of Webster and Banco Santander at:

Webster Financial Corporation	Banco Santander, S.A
200 Elm Street	Ciudad Grupo Santander
Stamford, Connecticut 06902 Attention: Investor Relations eharmon@websterbank.com	28660 Boadilla del Monte Spain Attention: Investor Relations investor@gruposantander.com
(212) 309-7646	+34 912899239

PARTICIPANTS IN THE SOLICITATION

Webster, Banco Santander and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from the stockholders of Webster in connection with the Transaction under the rules of the SEC. Information regarding the directors and executive officers of Webster and Banco Santander is set forth in (i) Webster’s definitive proxy statement for its 2025 Annual Meeting of Stockholders, including under the headings entitled “Director Nominees”, “Director Independence”, “Non-Employee Director Compensation and Stock Ownership Guidelines”, “Compensation and Human Resources Committee Interlocks and Insider Participation”, “Executive Compensation”, “2024 Pay Versus Performance” and “Security Ownership of Certain Beneficial Owners and Management”, which was filed with the SEC on April 11, 2025 and is available at https://www.sec.gov/ix?doc=/Archives/edgar/data/0000801337/000080133725000015/wbs-20250411.htm, and (ii) Banco Santander’s Annual Report on Form 20-F for the year ending December 31, 2024, including under the headings entitled “Directors and Senior Management”, “Compensation”, “Share Ownership” and “Majority Shareholders and Related Party Transactions”, which was filed with the SEC on February 28, 2025 and is available at https://www.sec.gov/ix?doc=/Archives/edgar/data/0000891478/000089147825000054/san-20241231.htm. To the extent holdings of each of Webster’s or Banco Santander’s securities by its directors or executive officers have changed since the amounts set forth in Webster’s definitive proxy statement for its 2025 Annual Meeting of Stockholders and in Banco Santander’s Annual Report on Form 20-F for the year ending December 31, 2024, such changes have been or will be reflected on Webster’s Statements of Change of Ownership on Form 4 filed with the SEC and on Banco Santander’s Annual Report on Form 20-F for the year ending December 31, 2025. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the definitive proxy statement/prospectus of Webster and Banco Santander and other relevant materials to be filed with the SEC when they become available. You may obtain free copies of these documents through the website maintained by the SEC at https://www.sec.gov.

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.

		Banco Santander, S.A.

Date:	February 25, 2026	By:	/s/ Pedro de Mingo Kaminouchi
			Name:	Pedro de Mingo Kaminouchi
			Title:	Head of Corporate Compliance

Banco Santander, S.A. 6-K