Claude Fable 5.1

Announced Sep 1, 2026Released

The update, in brief

Fable 5.1 supports demanding reasoning and long-horizon agentic work.

Generally available on Claude platforms; Mythos 5.1 has different access restrictions.

Availability and conditions refer to the original announcement.

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Demos, launch pages and discussions explicitly connected to this announcement.

Summarized from the linked sources. Availability refers to the announcement date.

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