Anthropic declined to submit its latest model, Claude Mythos 5.1, to Britain’s AI Security Institute for testing before release, prompting fears inside the UK government that tech companies are falling into line with the Trump administration’s AI protectionism. The $1tn company, which is gearing up for a blockbuster initial public offering in coming weeks, last week launched Claude Mythos 5.1, billed as its most advanced model in life sciences and cyber security. But for the first time the model was only made available to vetted US organisations, excluding the UK’s AI Security Institute (Aisi), the global leader in the testing of frontier models.

The decision not to offer pre-release access to Aisi, which has emerged as Britain’s most influential asset in the global AI race, has prompted alarm in Whitehall and inside the agency, according to UK government figures. National security officials have concerns. They definitely didn’t test Mythos 5.1.

There’s anxiety around it . . . They are worried this could be a sign of things to come with Aisi not being given access to the latest models.