White Mountains Insurance : 2026 Annual General Meeting

About this update from White Mountains Insurance Group, Ltd.

‌via email: [email protected]‌‌ Jennifer Moyer Chief Administrative Officer March 4, 2026 Barbara McWhirter Corporate Finance LOM Capital Limited The LOM Building 27 Reid Street Hamilton HM 11 Bermuda Dear Barbara: Please accept this letter as notice of this year's Annual Meeting arrangements: Company: White Mountains Insurance Group, Ltd. Meeting date: Thursday, May 21, 2026 Record date: Monday, March 30, 2026 Cusip number: G9618E107 Location: Hamilton Parish, Bermuda Please feel free to contact me at (603) 640-2210 if you have any questions or if I can provide any additional information relating to the meeting. Sincerely, Jennifer Moyer cc: Bermuda Stock Exchange: [email protected] WTM - John Sinkus [email protected] Corporate Headquarters: White Mountains Insurance Group, Ltd. A.S. Cooper Building, 26 Reid Street Hamilton HM 11, Bermuda Ph: 441-278-3160 ✯ Fax: 441-278-3170 Hanover Office: White Mountains Insurance Group, Ltd. 23 South Main Street, Suite 3B, Hanover, NH 03755 Ph: 603-640-2210 ✯ Fax: 603-640-2250 E-mail: [email protected]

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