The strange case of Dr Fable and Mr Mythos

A few days ago Anthropic released Claude Fable 5 and its older sibling Mythos 5. Frontier, agentic models, able to reason for hours over enormous codebases, to use tools autonomously, to behave almost like a senior software engineer. Fable 5 came out on Tuesday 9 June; by Friday the 12th, after about 72 hours of life, it was already gone. For a few hours – actually, for a few days – it was available to everyone. Then came the silence.

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