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

The new GPT-5.6 family: Luna, Terra, Sol - 9th July 2026
sqlite-utils 4.0, now with database schema migrations - 7th July 2026
sqlite-utils 4.0rc2, mostly written by Claude Fable (for about $149.25) - 5th July 2026

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

ai 2,111 openai 429 generative-ai 1,866 llms 1,833 anthropic 307 claude 289 ai-security-research 24 gpt 128

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