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.

Fable 5 promotion ends: included on Max, usage credits on Pro

The promotion that let paid plans spend up to 50% of weekly limits on Fable 5 ended on July 19, 2026. Fable models are now a standard part of Max and premium Team and Enterprise seats, while Pro and standard seats pay with usage credits.

Who is affected:

Pro and standard Team seat users of Fable 5 in the Claude apps and Claude Code.

Action needed:

Pro users who want Fable should turn on usage credits or switch to Opus.

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.

New Fable 5 safety classifier flags more benign coding requests

To redeploy Fable 5, Anthropic trained a stricter cyber classifier that blocks the reported bypass in over 99% of cases. Anthropic says it also flags benign requests more often during routine coding and debugging, and blocked requests go to Opus 4.8.

Who is affected:

Developers using Fable 5 for coding and debugging.

What to do:

Expect occasional fallbacks to Opus 4.8. Consider Opus 5 for security-adjacent code.

US government directive forces suspension of Fable 5 and Mythos 5

A US government export control directive, prompted by a reported method of bypassing Fable 5 safeguards found by Amazon researchers, led Anthropic to disable Fable 5 and Mythos 5 for all customers. Other models were not affected.

Who is affected:

All users of Claude Fable 5 and Claude Mythos 5 on every surface.

Action needed:

Switch to Claude Opus 4.8 until access returns.

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.

Fable 5 included in paid plans only through June 22

At launch, Anthropic said Fable 5 would be included in Pro, Max, Team and seat-based Enterprise plans through June 22, then require usage credits from June 23.

Who is affected:

Claude subscribers on Pro, Max, Team and seat-based Enterprise plans.

What to do:

Plan for usage credits if you rely on Fable 5 in the Claude apps.