Simon Willison Blog·Research·1d ago·~1 min read
Our evaluation of OpenAI's GPT-5.5 cyber capabilities
30th April 2026 - Link Blog
Our evaluation of OpenAI's GPT-5.5 cyber capabilities. The UK's AI Security Institute previously evaluated Claude Mythos: now they've evaluated GPT-5.5 for finding security vulnerability and found it to be comparable to Mythos, but unlike Mythos it's generally available right now.
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