Is Claude Mythos 5.1 out yet?
Yes.
About Claude Mythos 5.1
Rumored more-capable successor to Claude Mythos 5. Per an internal-portal note (June 22) and AI observer Andrew Curran, Anthropic reportedly finished training it ~9 days after the export-control suspension; may ship as Mythos 5.1 or Mythos 6, or stay internal to accelerate self-improvement. Unconfirmed by Anthropic.
How we confirmed it
Released via the API
September 1, 2026 at 12:00 PM UTC
An administrator marked this model available (silently).
Open detection source →Release timeline
- 2026-06-23 Official announcement or source
- 2026-10-13T14:11:27.547Z First official availability observed
- 2026-10-13T14:11:27.547Z Availability confirmed after the second check
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OutYet reporting
- Claude Fable 5.1 puts migration and data-retention choices in the foreground
Anthropic and AWS documentation put Claude Fable 5.1's migration behavior, cache economics, and safety-monitoring boundaries ahead of broad capability claims for technical buyers.
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Also waiting on: Gemini 3.5 Pro, GLM-6, Grok 5, Amazon Nova 2 Pro
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