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White Mountains Insurance Group Ltd was reported as having 127,993 shares beneficially owned by Vanguard Capital Management, representing 5.18% of the class as disclosed on a Schedule 13G. The filing states Vanguard Capital Management has sole dispositive power over 127,993 shares and sole voting power over 18,836 shares. The filing is signed by Ashley Grim on 04/30/2026 and includes a statement that ownership includes shares held for Vanguard funds and managed accounts.
White Mountains Insurance Group, through its operating company White Mountains Partners, has acquired a majority interest in BaseSix Systems LLC, a building systems integration and service provider. White Mountains’ equity investment in the deal was approximately $97 million, giving it control of a business focused on mission critical, low voltage systems for commercial and institutional customers across fire & life safety, network & wireless, security & access control, and audio-visual solutions.
Basesix, founded in 2018 and headquartered in Marietta, Georgia, has grown organically by delivering on-time, on-budget projects for complex integration needs and offering aftermarket service. Management from both organizations highlight plans to use the new capital partnership to support Basesix’s next growth phase, including potential new offices and strategic acquisitions.
White Mountains Insurance Group is asking shareholders to vote on three items at its 2026 annual meeting: electing four Class II directors to terms ending in 2029, approving an advisory vote on executive compensation, and ratifying PwC as independent auditor for 2026.
The proxy highlights a strong 2025, with book value per share reaching $2,188, up 25%, helped by the sale of Bamboo, which added roughly $320 per share, and about $200 million of share repurchases at accretive prices. Since its 1985 IPO, the company reports 13% annualized growth in book value per share and 12% in market value per share.
Operating businesses generally performed well, including Kudu’s 13% return on equity and HG Global’s $61 million of premiums, up 17%. The Board emphasizes governance practices such as 70% independent directors, an independent chair, 30% gender and 20% racial/ethnic diversity, and robust shareholder engagement, with outreach to holders of 75% of shares and meetings with holders of 31% of shares.
Executive pay is structured as pay-for-performance, with base salaries for named executive officers capped at $600,000 and 92% of 2025 CEO target compensation considered “at risk.” Long-term incentives are split between three-year cliff-vesting restricted shares and performance shares tied to compound growth in company value per share, with recent performance producing maximum or near-maximum payouts.
White Mountains Insurance Group Ltd — Schedule 13G/A amendment from The Vanguard Group. The filing states that, following an internal realignment effective January 12, 2026, certain Vanguard subsidiaries will report beneficial ownership separately. The Vanguard Group reports 0 shares beneficially owned and 0% of the class as of the amendment, reflecting disaggregation of holdings across affiliates.
The filing is signed by Ashley Grim, Head of Global Fund Administration, dated 03/27/2026.
WHITE MOUNTAINS INSURANCE GROUP LTD executive Robert Lawrence Seelig, EVP & General Counsel, made a bona fide gift of 50 Common Shares on 2026-03-19. The gift carried no sale proceeds. After this transfer, he directly holds 17,857 Common Shares and 2,500 restricted Common Shares, plus 4 Common Shares held indirectly by his wife and dependent children and 583 Common Shares held indirectly through the WTM Retirement Plan.
WHITE MOUNTAINS INSURANCE GROUP LTD director David Allen Tanner reported a disposition of shares through a bona fide gift. He transferred 225 common shares at a stated price of $0.00 per share on this Form 4. After the gift, he directly owns 1,879 common shares.
Caffrey Liam P reported acquisition or exercise transactions in this Form 4 filing.
WHITE MOUNTAINS INSURANCE GROUP LTD reported that Chief Executive Officer Liam P. Caffrey received a grant of 1,500 restricted common shares on February 25, 2026. The award carries no purchase price and is scheduled to vest on January 1, 2029, functioning as stock-based compensation.
Following this grant, Caffrey directly holds 3,650 common shares in total, which includes both restricted and unrestricted stock, and also has 8 common shares held indirectly through the WTM Retirement Plan. The filing does not show any open‑market buying or selling, only this equity award and updated holdings.
Harrison Giles E reported acquisition or exercise transactions in this Form 4 filing.
WHITE MOUNTAINS INSURANCE GROUP LTD President Giles E. Harrison reported an equity grant in the form of 775 restricted common shares on February 25, 2026. The award carried a grant price of $0.00 per share and is scheduled to vest on January 1, 2029.
After this grant, his directly held common shares increased to 2,675. In addition, he indirectly holds 2 common shares through a company retirement plan account, reflecting accumulation in that plan report dated as of February 25, 2026.
Hildreth Michaela reported acquisition or exercise transactions in this Form 4 filing.
WHITE MOUNTAINS INSURANCE GROUP LTD executive Michaela Hildreth, MD & Chief Accounting Officer, reported receiving a grant of 600 restricted Common Shares on February 25, 2026, at a price of $0.00 per share. The award will vest on January 1, 2029.
After this grant, she directly held 1,825 restricted Common Shares. As of the same date, she also directly held 2,491 Common Shares and indirectly held 20 Common Shares through a 401(k) account.