Pedro J. Bermeo
Davis Polk & Wardwell LLP

450 Lexington Avenue

New York, New York 10017

+1 (212) 450-4000

Jeffrey Cohen

Linklaters LLP

1290 Avenue of the Americas

New York, NY 10104

+1 (212) 903-9014

Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

third-party tender offer subject to Rule 14d-1.

issuer tender offer subject to Rule 13e-4.

going-private transaction subject to Rule 13e-3.

amendment to Schedule 13D under Rule 13d-2.

Rule 13e-4(i) (Cross-Border Issuer Tender Offer)

Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)

Name and Address. The name of the subject company and Offeror is Banco Santander, S.A. The principal office of the Offeror is located at Ciudad Grupo Santander 28660, Boadilla del Monte (Madrid), Spain. The telephone number of the Offeror is +34 91 276 92 90.

Securities. The subject securities are the Securities. As of May 27, 2026, $1,000,000,000 of the Securities were outstanding.

Trading Market and Price. The information set forth in the Offer to Purchase in the section entitled “Market Information and Dividend Policy—Securities” is incorporated by reference herein.

Name and address. The Offeror is the filing person and the subject company. The Offeror’s address and telephone number are set forth in Item 2(a) above.

Name

Title

Director Since

Name

Title

Material Terms. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer,” “The Offer” and “Taxation Considerations” is incorporated by reference herein.

Tender Offers.

The total number and class of securities sought in the offer. The information set forth in the Offer to Purchase on the front cover page and in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

The type and amount of consideration offered to security holders. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

The scheduled expiration date. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

Whether a subsequent offering period will be available, if the transaction is a third-party tender offer. Not applicable.

Whether the offer may be extended, and if so, how it could be extended. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

The dates before and after which security holders may withdraw securities tendered in the offer. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

The procedures for tendering and withdrawing securities. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

The manner in which securities will be accepted for payment. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

If the offer is for less than all securities of a class, the periods for accepting securities on a pro rata basis and the offeror’s present intentions in the event that the offer is oversubscribed. The information set forth in the Offer to Purchase in the sections entitled “Summary Terms of the Offer” and “The Offer” is incorporated by reference herein.

An explanation of any material differences in the rights of security holders as a result of the transaction, if material. Not applicable.

A brief statement as to the accounting treatment of the transaction, if material. Not applicable.

The federal income tax consequences of the transaction, if material. The information set forth in the Offer to Purchase in the section entitled “Taxation Considerations—Material U.S. Federal Income Tax Considerations” is incorporated by reference herein.

Mergers or Similar Transactions. Not applicable.

Purchases. To the Offeror’s knowledge based on reasonable inquiry, no Securities are owned by any officer, director or affiliate of the Offeror, and therefore, no Securities will be purchased from any officer, director or affiliate of the Offeror in connection with the Offer.

Agreements involving the subject company’s securities. The Offeror has entered into an indenture dated as of May 12, 2021 (the “Base Indenture”) between the Offeror, as issuer, and The Bank of New York Mellon, London Branch, as trustee (the “Trustee”), as supplemented by a first supplemental indenture dated as of May 12, 2021 (the “First Supplemental Indenture”) between the Offeror, as issuer, and the Trustee (each of which is filed as an exhibit to this Schedule TO) relating to the Securities.

Purposes of the transaction. The information set forth in the Offer to Purchase in the sections entitled “Rationale of the Offer” and “The Offer—Purpose of the Offer” are incorporated by reference herein.

Use of securities acquired. The Securities purchased pursuant to the Offer will be canceled following settlement of the Offer.

Plans. There are no plans, proposals or negotiations that relate to or would result in any of the effects or circumstances described in Items (1), (2), (3), (4), (5), (6), (7), (8), (9) or (10) of Item 1006(c) of Regulation M-A.

Source of Funds. The Offeror will use the proceeds from a concurrent offering of new AT1 securities or available cash to pay the tender consideration, any accrued distribution and other expenses associated with the Offer. The information set forth in the Offer to Purchase in the sections entitled “The Offer—Terms of the Offer—Source of Funds” is incorporated by reference herein.

Conditions. The information set forth in the Offer to Purchase in the sections entitled “The Offer—Terms of the Offer—Source of Funds” is incorporated by reference herein.

Borrowed Funds. The information set forth in the Offer to Purchase in the sections entitled “The Offer—Terms of the Offer—Source of Funds” is incorporated by reference herein.

Securities Ownership. None of the Offeror, its affiliates, its directors or executive officers owns any Securities.

Securities Transactions. None of the Offeror, its affiliates, its directors or executive officers has purchased any Securities for its or their own account.

Solicitations or Recommendations. The information in the Offer to Purchase under the headings “Summary Terms of the Offer,” “The Offer— Dealer Manager and Tender Agent” and “The Offer—Terms of the Offer—No Recommendation” is incorporated by reference herein.

Financial Information. The following financial statements and information are incorporated by reference herein:

The Offeror’s Report on Form 6-K furnished to the SEC on April 1, 2026 relating to certain recast financial information as a result of certain changes to the presentation of the Offeror’s’s financial information (accession no. 0000891478-26-000037) (the “Recast 6-K”);

The Offeror’s 2025 Annual Report on Form 20-F for the year ended December 31, 2025 filed with the SEC on February 27, 2026 (except with respect to the information and the audited financial statements included therein and superseded by the information and the audited financial statements included in the Recast 6-K);

Sections 3 and 4 under “Part 1. Consolidated Directors’ Report-Economic and Financial Review” in the the Offeror’s annual report on Form 20-F for the year ended December 31, 2024 filed with the SEC on February 28, 2025 (except with respect to the information included therein and superseded by the information included in the Recast 6-K);

the Offeror’s Report on Form 6-K filed with the SEC on April 29, 2026 (accession no. 0000891478-26-000048); and

the Offeror’s Report on Form 6-K filed with the SEC on April 29, 2026 (accession no. 0000891478-26-000053).

Pro Forma Information. Not applicable.

Agreements, regulatory requirements and legal proceedings.

None.

The Offeror is required to comply with U.S. federal and state securities laws and tender offer rules in connection with the Offer.

Not applicable.

Not applicable.

None.

Other material information. The information set forth in the Offer to Purchase is incorporated by reference herein.

Number

Description

(a)(2)

(a)(3)

(a)(4)

(a)(5)

(b)

(d)(1)

(d)(2)

(g)

(h)

Fee Exhibit*

Filed herewith.