Security Research

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.

The UK's AI Security Institute has evaluated OpenAI's GPT-5.5 for security vulnerability detection capabilities. The evaluation found GPT-5.5 performs comparably to Anthropic's Claude Mythos, with the key distinction that GPT-5.5 is generally available while Mythos remains in limited release.