Claude Fable 5 changelog

Claude Fable 5.1 released as the successor to Fable 5

Claude Fable 5.1 (and Claude Mythos 5.1 for Project Glasswing participants) launched at the same $10 / $50 per million tokens as Fable 5, with cache reads cut to $0.25 per million tokens.

Who is affected:

Teams using Claude Fable 5 on the API or in the Claude apps.

What to do:

Move from claude-fable-5 to claude-fable-5-1 after checking the tool_choice and thinking-block changes.

Access to Claude Fable 5 restored after export controls lifted

Fable 5 returned on July 1 on the Claude Platform, Claude.ai, Claude Code and Claude Cowork. Paid plans could use it for up to 50% of weekly limits through July 7. Mythos 5 returned for a set of US organizations.

Who is affected:

Everyone who used Fable 5 before the June 12 suspension.

What to do:

Re-enable Fable 5 in your app or model picker. Note new safeguards may flag more benign requests.

Claude Fable 5 released, with Claude Mythos 5 for Glasswing partners

Claude Fable 5 launched as a generally available Mythos-class model at $10 / $50 per million tokens, with safety classifiers that route some requests to Claude Opus 4.8. Claude Mythos 5 is the same model with fewer safeguards, limited to Project Glasswing partners.

Who is affected:

Anyone choosing a top-tier Claude model on the API or in the Claude apps.

What to do:

Expect some cyber-related requests to fall back to Opus 4.8, and plan for 30-day data retention on the API.