Company: AHL
Filing Date: 2025-08-27
Form Type: 6-K
Source: 0001267395-25-000058
Chunk: 0

Company: ASPEN INSURANCE HOLDINGS LTD
Filing Date: 2025-08-27
Form: 6-K
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### Form 6-K
<div align='center'>REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES</div>

#### EXCHANGE ACT OF 1934
<div align='center'>For the month of August 2025

Commission File Number: 001-31909</div>

### ASPEN INSURANCE HOLDINGS LIMITED
<div align='center'>(Translation of registrant’s name into English)</div>

#### 141 Front Street

#### Hamilton HM 19

#### Bermuda
<div align='center'>(Address of principal executive office)</div>

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F ý Form 40-F ¨

#### ENTRY INTO MERGER AGREEMENT
On August 27, 2025, Aspen Insurance Holdings Limited, a Bermuda exempted company limited by shares (“ Aspen ”) (NYSE: AHL) entered into a definitive agreement under which Aspen will be acquired by a wholly owned indirect subsidiary of Sompo Holdings, Inc., a leading global provider of commercial and consumer property and casualty (re)insurance.

The Agreement and Plan of Merger (the “ Merger Agreement ”) is by and among Aspen, Endurance Specialty Insurance Ltd., a Bermuda exempted company limited by shares (“ Parent ”), and Ajax Ltd., a Bermuda exempted company limited by shares and a wholly owned subsidiary of Parent (“ Merger Sub ”). The Merger Agreement provides that, subject to the satisfaction or waiver of certain conditions set forth therein, and in the statutory merger agreement (the “ Statutory Merger Agreement ”), Merger Sub will merge with and into Aspen in accordance with the Companies Act 1981 of Bermuda (the “ Bermuda Companies Act ”), with Aspen surviving such Merger (the “ Merger ” and such surviving company, the “ Surviving Company ”) as a wholly owned subsidiary of Parent.

At the effective time of the Merger (the “ Effective Time ”), each issued Class A ordinary share, par value $0.001 per share, of Aspen (each, a “ Company Share ”) (other than any Company Share held by Aspen or any subsidiary thereof as treasury shares or any Company Share owned by Parent, Merger Sub or any other direct or indirect