Simon Willison’s Weblog

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.

Posted 30th April 2026 at 11:03 pm

Recent articles

Live blog: Code w/ Claude 2026 - 6th May 2026
Vibe coding and agentic engineering are getting closer than I'd like - 6th May 2026
LLM 0.32a0 is a major backwards-compatible refactor - 29th April 2026

This is a link post by Simon Willison, posted on 30th April 2026.

ai 2005 openai 417 generative-ai 1777 llms 1742 anthropic 280 claude 274 ai-security-research 16 gpt 124

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