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

Generating running routes with GPT-6 Astra and ChatGPT Work - 12th September 2026
OpenAI agents attacked RubyGems back in May - 12th September 2026
Some thoughts on the Navier–Stokes Millennium Prize Problem - 8th September 2026

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

ai 2,242 openai 464 generative-ai 1,988 llms 1,954 anthropic 338 claude 311 ai-security-research 42 gpt 131

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