Klaviyo, Inc.

Disclosure in lieu of reporting on a Current Report on Form 8-K

On October 31, 2025, the Company entered into an Employee Assignment Agreement with Velocity Global Switzerland GmbH (“Velocity”) pursuant to which, effective November 5, 2025, Velocity will serve as the legal employer of record of Chano Fernández, the Company’s Interim Executive Officer, and on October 31, 2025, Mr. Fernández entered into a corresponding employment agreement with Velocity. Mr. Fernández’s employment agreement has an indefinite term. Under the Employee Assignment Agreement and the Company’s Master Services Agreement with Velocity Global LLC dated September 10, 2020, Velocity will make Mr. Fernández’s services available to the Company, and the Company will reimburse Velocity for the compensation and benefits it provides to Mr. Fernández. In conjunction with Mr. Fernández’s transition to Velocity, his employment with Klaviyo Ltd will terminate. As an employee of Velocity, Mr. Fernández will be entitled to receive an annual base salary of 800,000 CHF.

Securities Trading Plans of Directors or Executive Officers

(c)During the three months ended September 30, 2025, certain of the Company’s directors and officers (as defined in Rule 16a-1(f) under the Exchange Act)adopted written plans intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) of the Exchange Act for the sale of the Company’s securities, as set forth in the table below.

No other directors or officers (as defined in Rule 16a-1(f) under the Exchange Act)adopted, modified and/orterminated a “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement,” as defined in Regulation S-K Item 408, during the three months ended September 30, 2025.