UK AI Security Institute Evaluates OpenAI's GPT-5.5 Cyber Capabilities
The UK's AI Security Institute has evaluated OpenAI's GPT-5.5 for finding security vulnerabilities, finding it comparable to Claude Mythos. Unlike Mythos, GPT-5.5 is generally available now. The evaluation was conducted by the UK AI Security Institute, which previously evaluated Claude Mythos. The findings were shared by Simon Willison in a link post on 30th April 2026.
Key facts
- UK AI Security Institute evaluated OpenAI's GPT-5.5
- GPT-5.5 found comparable to Claude Mythos for security vulnerability detection
- GPT-5.5 is generally available now, unlike Mythos
- Previous evaluation of Claude Mythos by the same institute
- Simon Willison posted about this on 30th April 2026
- Post is a link post on simonwillison.net
Entities
Institutions
- UK AI Security Institute
- OpenAI
Locations
- United Kingdom