Introducing Claude Fable 5: a Mythos-class model made safe for general use
Claude @claudeai · x · 2026-06-09 · ★★★★★ · archived
The launch post for Anthropic's first publicly available Mythos-class model, which the US government suspended three days later.
Summary
The official Claude account announced Fable 5 as a Mythos-class model 'made safe for general use', with capabilities above any model Anthropic had made generally available. The thread says it is SOTA on nearly all tested benchmarks and pulls further ahead on longer tasks. Safeguards on cyber, bio/chem and distillation fall back to Opus 4.8 in under 5% of sessions. Claude Mythos 5, the same model with some safeguards lifted, went to vetted cyber defenders and critical-infrastructure operators. Staff launch posts include Felix Rieseberg (x.com/felixrieseberg/status/2064392202504310900), Mike Krieger (x.com/mikeyk/status/2064392825480032418) and Boris Cherny (x.com/bcherny/status/2064402671898075579), all verified. Verified via syndication: 2026-06-09T17:08:13Z.
Archived text
Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use.
Its capabilities exceed those of any model we’ve ever made generally available. https://t.co/2AvmEjHIX8
Media: https://pbs.twimg.com/media/HKY5eixXIAE9EAZ.jpg
likes 103766 · replies 4939 (at fetch time)
Archived 2026-09-29 via syndication.
Related events
- Anthropic releases Claude Fable 5 and Claude Mythos 5 — first generally available Mythos-class model 2026-06-09
- US export controls force Anthropic to suspend Claude Fable 5 / Mythos 5; access restored July 1 2026-06-12
All posts · id: 2026-06-09-claudeai-introducing-fable-5