Cybersecurity

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.

OpenAI released GPT-5.5-Cyber in limited preview on Thursday, a variant of its GPT-5.5 model with relaxed safeguards for vetted cybersecurity teams. The model is trained to be more permissive on security-related tasks including vulnerability identification, patch validation, and malware analysis.

OpenAI is providing a less-restricted version of GPT-5.5 to vetted cybersecurity defenders through its Trusted Access for Cyber program. The model, dubbed GPT-5.5-Cyber, completed a 32-step simulated corporate cyberattack in 2 out of 10 test runs according to the U.K. AI Security Institute, narrowly trailing Anthropic's Mythos which succeeded in 3 out of 10 attempts.

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.