6-K

SECURITIES AND EXCHANGECOMMISSION

Washington, D.C. 20549

Form 6-K

Report of Foreign Issuer

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

the Securities Exchange Act of 1934

For the month of December 2025

Eni S.p.A.

(Exact name of Registrant as specified in its charter)

Piazzale Enrico Mattei 1 - 00144 Rome, Italy

(Address of principal executive offices)

(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 x    Form 40-F ¨

(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 12g3-2b under the Securities Exchange Act of 1934.)

Yes ¨     No x

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

Table of contents

SIGNATURES

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, hereunto duly authorised.

Date: December 31, 2025

Eni: report on the purchase of treasury sharesduring the period from 22 to 23 December 2025

San Donato Milanese (Milan), 31 December 2025 – During the period from 22 to 23 December 2025, Eni acquired on the Euronext Milan no. 1,875,245 shares (equal to 0.06% of the share capital), at a weighted average price per share equal to 16.0207 euro, for a total consideration of 30,042,721.20 euro within the treasury shares program approved by the Shareholders' Meeting on 14 May 2025, previously subject to disclosure in accordance with applicable legislation.

On the basis of the information provided by the intermediary appointed to make the purchases, here below a synthesis of transactions for the purchase of treasury shares on the Euronext Milan on a daily basis:

From the start on 20 May 2025 of the buyback program, Eni acquired no. 101,010,847 shares (equal to 3.21% of the share capital) for a total consideration of 1,499,999,997.68 euro.

Considering the treasury shares already held and the purchases made and the free of charge shares granted to Eni’s executives (following the conclusion of the Vesting Period as provided by the “Long-Term Incentive Plan 2020-2022” approved by Eni’s Shareholders’ Meeting of 13 May 2020) and to Eni’s employees (as provided by the “Employee Stock Ownership Plan” approved by Eni’s Shareholders’ Meeting of 15 May 2024), Eni holds n. 187,838,861 shares equal to 5.97% of the share capital.

Details of the daily transactions made during the period from 22 to 23 December 2025 are reported below.