On June 9, 2026, Anthropic introduced a new top-tier model class called "Mythos," releasing the general-availability Claude Fable 5 and the restricted Claude Mythos 5. The move replaces "Opus" as the highest model class, with Mythos applying from the Claude 5 series onward. Fable 5 packages a "Mythos-class model" in a form safe for general use, while Mythos 5 is an upper-tier version of the same foundation model with certain safeguards—such as those around cybersecurity—partially lifted (announcement, platform docs).
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