UK AISI

A month after its initial release, a newer checkpoint of Anthropic's Mythos Preview became the first model to complete the UK AI Safety Institute's 'Cooling Tower' cyber range, solving it in 3 of 10 attempts. The model also completed 'The Last Ones' range in 6 of 10 attempts, surpassing OpenAI's GPT-5.5 and demonstrating capability improvements within a single model version.

Anthropic is restricting access to Claude Mythos Preview, a model the company claims can find security vulnerabilities better than most humans, to 52 technology partners. While the UK's AI Security Institute has already tested Mythos and published findings, most European cybersecurity agencies have limited or no access, revealing a structural gap in Europe's AI safety evaluation capacity.