{"filing":{"accession_number":"0001628280-26-059191","cik":"0000776867","ticker":"WTM","company_name":"WHITE MOUNTAINS INSURANCE GROUP LTD","form":"8-K","filing_date":"2026-08-27","report_date":"2026-08-26","primary_document":"wtm-20260826.htm","primary_document_url":"https://www.sec.gov/Archives/edgar/data/776867/000162828026059191/wtm-20260826.htm"},"events":[{"id":29922,"run_id":27420,"accession_number":"0001628280-26-059191","anchor_item_number":"5.02","event_type":"exec_appointment","event_domain":"governance","is_material":true,"confidence":0.95,"summary":"The Board of Directors elected Stephen Klar as a director on August 26, 2026, increasing the Board size from 10 to 11 persons. This is a clear appointment of a director to the Company's Board. While the disclosure also mentions standard compensatory arrangements for non-employee directors, the principal disclosed action is the election and appointment of Mr. Klar to the Board, making this an exec_appointment event. The appointment of a new director with significant financial services experience (formerly President and Managing Partner of Wellington Management Group LLP) is material to investors' assessment of the Company's governance and leadership.","company_name":"WHITE MOUNTAINS INSURANCE GROUP LTD","ticker":"WTM","filing_date":"2026-08-27","form":"8-K","submitted_at":null,"items":[{"id":32362,"accession_number":"0001628280-26-059191","item_number":"5.02","item_title":"Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.","event_type":"exec_appointment","event_domain":"governance","is_material":true,"confidence":0.95,"reasoning":"The Board of Directors elected Stephen Klar as a director on August 26, 2026, increasing the Board size from 10 to 11 persons. This is a clear appointment of a director to the Company's Board. While the disclosure also mentions standard compensatory arrangements for non-employee directors, the principal disclosed action is the election and appointment of Mr. Klar to the Board, making this an exec_appointment event. The appointment of a new director with significant financial services experience (formerly President and Managing Partner of Wellington Management Group LLP) is material to investors' assessment of the Company's governance and leadership.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-08-27T12:12:40.067605+00:00","company_name":"","ticker":null,"filing_date":""}]}],"classifications":[{"id":32362,"accession_number":"0001628280-26-059191","item_number":"5.02","item_title":"Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.","event_type":"exec_appointment","event_domain":"governance","is_material":true,"confidence":0.95,"reasoning":"The Board of Directors elected Stephen Klar as a director on August 26, 2026, increasing the Board size from 10 to 11 persons. This is a clear appointment of a director to the Company's Board. While the disclosure also mentions standard compensatory arrangements for non-employee directors, the principal disclosed action is the election and appointment of Mr. Klar to the Board, making this an exec_appointment event. The appointment of a new director with significant financial services experience (formerly President and Managing Partner of Wellington Management Group LLP) is material to investors' assessment of the Company's governance and leadership.","classifier_version":"claude-haiku-4-5-20251001+prompt-a85dd512","taxonomy_version":"v1.3","classified_at":"2026-08-27T12:12:40.067605+00:00","company_name":"WHITE MOUNTAINS INSURANCE GROUP LTD","ticker":"WTM","filing_date":"2026-08-27"}]}