On 25 July 2024, the United States and the United Kingdom signed a new amendment to their Mutual Defense Agreement. The agreement, concluded in 1958, has been regularly amended since. The current version of the agreement that consolidates the amendments through 2024 is in the IPFM Library (see also an annotated text compiled by Nuclear Information Service).

The key change in the 2024 amendment is that it removed the end-date requirement for the transfer of special nuclear materials and equipment (Article IIIbis). The 2014 version of the agreement specified the following:

C. The Government of the United States shall transfer enriched uranium, and shall arrange enrichment and other uranium services to the Government of the United Kingdom, for military purposes, in such quantities, at such times prior to December 31, 2024, and on such terms and conditions as may be agreed.

In the 2024 version, this paragraph looks as follows:

C. The Government of the United States shall transfer enriched uranium to the Government of the United Kingdom, and shall arrange enrichment and other uranium services to the Government of the United Kingdom, for military purposes, in such quantities, at such times, and on such terms and conditions as may be agreed.

UPDATE: The agreement entered into force on 14 November 2024.