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Only a month after its initial release, Anthropic's storied Mythos model is breaking new testing boundaries.
Anthropic's Claude Mythos, which the company maintains is too powerful to be released generally, already appears to have gained new capabilities.
In a blog post published Wednesday, the UK AI Security Institute (AISI) reported that it had tested a newer version of Mythos, which outperformed both its earlier results and OpenAI's GPT-5.5 -- just a month after Mythos' initial release.