White Mountains Insurance Group Ltd.

ITEM 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On August 26, 2026, the Board of Directors (the “Board”) of White Mountains Insurance Group, Ltd. (the “Company”) elected Stephen Klar as a director of the Company. In connection with Mr. Klar’s election, the size of the Board was increased from 10 to 11 persons. Mr. Klar will hold office as a director on the Board until the Company’s next annual meeting of shareholders and until his successor is elected and qualified or until his earlier resignation or removal. Mr. Klar will receive compensation for his service on the Board in accordance with the Company’s standard compensatory arrangement for non-employee directors, including a pro-rated cash and common equity retainer for the remainder of the current year. A description of the Company’s non-employee director compensation appears under the caption “Director Compensation” in the Company’s Proxy Statement filed with the Securities and Exchange Commission on April 1, 2026. There are no arrangements or understandings between Mr. Klar and any other persons pursuant to which he was elected as a director. Mr. Klar has no direct or indirect material interest in any transaction required to be disclosed pursuant to Item 404(a) of Regulation S-K. Our press release announcing Mr. Klar’s election as director is attached as Exhibit 99.1 and incorporated by reference herein.