Next Mythos-Class Model released by September 4, 2026?

Realized · held to resolution+43%$100 paper stake

Polymarket70¢ → 100¢

Our position · YES70¢ → 100¢

Signal endedSep 1

Forecast updatedSep 1

Aug 30 forecast

Background routing signs point to an unannounced Fable update that could become publicly labeled quickly, so a qualifying Mythos-class release by September 4 is likely.

The visible official evidence leans against release: Mythos 5 remained restricted, while Opus 5 was still Anthropic’s most capable generally available model. Even so, apparent background routing to Fable 5.1 suggests deployment may precede public naming, and Anthropic has recently shipped other models in quick succession. A qualifying release is therefore likely with meaningful uncertainty, especially because only days remain and no official announcement has surfaced.

Points to YES

Independent monitoring found signs that Fable 5.1 was already entering background deployment, although Anthropic had not confirmed that interpretation.
On August 26, @testingcatalog assessed that more users appeared to be routed from Claude Fable 5 to Claude Fable 5.1 in the background.
Anthropic’s recent succession of major model launches shows that another release can follow quickly.
Anthropic launched Claude Sonnet 5 on June 30 and Claude Opus 5 on July 24.

Points to NO

Claude Mythos 5 remained confined to approved customers rather than the general public.
On August 25, Anthropic’s migration guide said Claude Mythos 5 was available only to approved Project Glasswing customers.
Anthropic’s public model lineup still placed Opus 5 above any generally available successor in the relevant class.
As of August 18, Anthropic described Opus 5, rather than a newer Mythos-class model, as its most capable generally available model.
Federal pre-release vetting could delay public access to an advanced model even after technical deployment begins.
On June 24, a U.S. executive order established a framework allowing federal vetting of the most advanced AI systems for up to one month before public release.

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