wtm-20251205

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

December 5, 2025

Date of Report (Date of earliest event reported)

WHITE MOUNTAINS INSURANCE GROUP, LTD.

(Exact name of registrant as specified in its charter)


Bermuda (State or other jurisdiction of incorporation or organization)			1-8993 (Commission file number)			94-2708455 (I.R.S. Employer Identification No.)

23 South Main Street, Suite 3B, Hanover, New Hampshire 03755

(Address of principal executive offices)

(603) 640-2200

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Shares, par value $1.00 per share

WTM

New York Stock Exchange

WTM.BH

Bermuda Stock Exchange

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933(§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

ITEM 2.01. Completion of Acquisition or Disposition of Assets.

On December 5, 2025, White Mountains Insurance Group, Ltd. (“White Mountains”) completed the previously announced sale of a controlling financial interest in WM Pierce Holdings, Inc. and its subsidiaries, including Bamboo Ide8 Insurance Services, LLC, (collectively, the “Bamboo Group”), to affiliates of funds advised by CVC Capital Partners (“CVC”), pursuant to the terms of the securities purchase agreement dated October 2, 2025 (the “Bamboo SPA”). Under the terms of the Bamboo SPA, a wholly owned subsidiary of White Mountains sold approximately 77.3% of its equity interest in the Bamboo Group for net cash proceeds at closing of $848 million and retained an indirect equity interest valued at $250 million (the “Bamboo Sale Transaction”).

ITEM 8.01. Other Events.

On December 8, 2025, White Mountains issued a press release announcing the closing of the Bamboo Sale Transaction. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K.

ITEM 9.01. Financial Statements and Exhibits.

Pro Forma Financial Information

White Mountains is filing as Exhibit 99.2 to this Current Report on Form 8-K the following unaudited pro forma condensed consolidated financial information, which is based on the historical financial statements of White Mountains and its consolidated subsidiaries, adjusted to give effect to the Bamboo Sale Transaction:

(1) Unaudited pro forma condensed consolidated balance sheet as of September 30, 2025; and

(2) Unaudited pro forma condensed consolidated statements of operations for the nine months ended September 30, 2025 and the year ended December 31, 2024.

Exhibits

99.1 Press Release, dated Dece mber 8 , 2025

99.2 Unaudited pro forma condensed consolidated financial statements

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

WHITE MOUNTAINS INSURANCE GROUP, LTD.

December 8, 2025

By:

/s/ MICHAELA J. HILDRETH

Michaela J. Hildreth

Managing Director and

Chief Accounting Officer

White Mountains Insurance Group Ltd. filed SEC Form 8-K: Completion of Acquisition or Disposition of Assets, Other Events, Financial Statements and Exhibits