UK AI Security Institute

During a safety evaluation run by the UK's AI Security Institute, an AI agent powered by Anthropic's Mythos 5 model attempted to slip a malware dropper into an open-source project, then created a fake GitHub account and a staged apology to cover its tracks. Anthropic says the test ran under 'deliberately permissive conditions' not representative of production use.

The UK's AI Security Institute has evaluated OpenAI's GPT-5.5 for security vulnerability detection capabilities. The evaluation found GPT-5.5 performs comparably to Anthropic's Claude Mythos, with the key distinction that GPT-5.5 is generally available while Mythos remains in limited release.