Next Mythos-Class Model released by September 3, 2026?

ResolutionResolved YES

YES payout100¢

NO payout0¢

VenuePolymarket

Realized · held to resolution+35%$100 paper stake

Polymarket74¢ → 100¢

Our position · YES74¢ → 100¢

Signal endedSep 1

Forecast updatedSep 1

Bedrock traces and resumed security evaluations suggest advanced launch preparation, so Anthropic’s next Mythos-class public release by September 3 is likely.

The visible evidence still leans against an on-time release: Anthropic had not confirmed Fable 5.1, its catalogue omitted the model, and an anticipated August launch passed. Even so, a Bedrock response pattern consistent with prerelease registration, restarted cybersecurity evaluations, and Anthropic’s earlier promise of more capable models in the coming months support a short-notice launch. The limited time and unresolved safety work leave meaningful uncertainty, but public availability by the cutoff remains the most likely outcome.

Points to YES

A Bedrock response pattern is consistent with Claude Fable 5.1 being registered but not yet provisioned.
On August 31, ArkeonTech assessed that changes in Amazon Bedrock responses indicated Fable 5.1 was registered but not yet provisioned.
Anthropic has restarted cybersecurity evaluations of prerelease models under strengthened safeguards.
By August 31, Anthropic’s external and internal cybersecurity evaluations were running again with new containment and monitoring practices.

Points to NO

Anthropic’s public catalogue still showed no Claude Fable 5.1 model immediately before the window’s final days.
On August 31, Anthropic’s model catalogue listed four models and did not include Fable 5.1.
The circulated Melon and Marshmallow identifiers remain unconfirmed as final consumer models.
As of August 31, Anthropic had not publicly defined the identifiers or confirmed that either represented a model headed for launch.
Some higher-risk training environments remain paused, indicating that safety work could still delay release clearance.
As of August 31, some high-risk reinforcement-learning environments for Anthropic’s prerelease models remained paused pending manual review or updated safeguards.

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