Anthropic Withheld Mythos 5.1 From UK AI Security Institute Pre-Release Testing
IT Pro·high signal
Per the Financial Times, Anthropic gave vetted US organizations pre-release access to Mythos 5.1, the restricted-access sibling of Fable 5.1 launched September 1, but did not give it to the UK AI Security Institute. It is the first time AISI has been excluded from an Anthropic frontier release, and the Cabinet Office has ordered an urgent assessment amid concern about a wider protectionist shift among US labs. Some UK officials suspect pressure from Washington, which remains unconfirmed.