Company: BCDRF
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260533
Chunk: 0

Company: Banco Santander, S.A.
Filing Date: 2025-10-31
Form: 424B5
Chunk 0
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Filed Pursuant to Rule 424(b)(5)
Registration Statement No. 333-271955

PROSPECTUS SUPPLEMENT

(to prospectus dated May 16, 2023)

$2,800,000,000

Banco Santander, S.A.

$300,000,000 Senior Non Preferred Floating Rate Notes due 2030

$1,250,000,000 4.551% Senior Non Preferred Fixed Rate Notes due 2030

$1,250,000,000 5.127% Senior Non Preferred Fixed Rate Notes due 2035

We are offering $300,000,000 principal amount of Senior Non Preferred Floating Rate Notes due 2030 (the “2030 Floating Rate
Notes”), $1,250,000,000 principal amount of 4.551% Senior Non Preferred Fixed Rate Notes due 2030 (the “2030 Fixed Rate Notes”), and $1,250,000,000 principal amount of 5.127% Senior Non Preferred Fixed Rate Notes due 2035 (the
“2035 Fixed Rate Notes” and, together with the 2030 Floating Rate Notes and the 2030 Fixed Rate Notes, the “Notes”).

The 2030 Floating Rate Notes will bear interest at the 2030 Floating Rate Interest Rate (as defined herein). From and including the date of
issuance, interest will be payable quarterly in arrears on the 2030 Floating Rate Notes on February 6, May 6, August 6 and November 6 of each year, beginning on February 6, 2026. Unless we redeem the 2030 Floating Rate Notes
earlier, the 2030 Floating Rate Notes will be due on November 6, 2030.

The 2030 Fixed Rate Notes will bear interest at a rate of
4.551% per year. From and including the date of issuance, interest will be payable semi-annually in arrears on the 2030 Fixed Rate Notes on May 6 and November 6 of each year, beginning on May 6, 2026. Unless we redeem the 2030 Fixed
Rate Notes earlier, the 2030 Fixed Rate Notes will be due on November 6, 2030.

The 2035 Fixed Rate Notes will bear interest at a rate
of 5.127% per year. From and including the date of issuance, interest will be payable semi-annually in arre