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A model-access console on a security operations centre desk listing Claude Fable 5.1 and Claude Mythos 5.1, the Mythos row marked restricted, a badge caught mid-tap against a reader beside the keyboard

One Model, Two Names: How Anthropic Splits Fable From Mythos

Claude Fable 5.1 and Claude Mythos 5.1 are the same weights wearing two different sets of restrictions — and which name you get depends less on what you're building than on who Anthropic and the US government believe you are.

By Brecht Corbeel · September 1, 2026 · 13 min read

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