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

Qwen 3.8 27B is excellent, but it defaults to wildly overthinking things - 16th August 2026
Now we have a timeline of the OpenAI accidental attack against Hugging Face - 7th August 2026
One-shotting a Raccoon Heist game using Claude Fable 5 - 5th August 2026

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

ai 2,191 openai 447 generative-ai 1,940 llms 1,907 anthropic 328 claude 300 ai-security-research 37 gpt 131

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