METR Files Confirm Fable 5.2 Is "Model 3"; Stronger Unreleased Model May Exist

METR report and system card screenshots confirm Claude Fable/Mythos 5.2 is the same snapshot as "Model 3 Early" from METR's September pre-deployment evals, showing 1.9x capability acceleration. The cards also reference an "internal model," fueling speculation that Anthropic holds a stronger unreleased model.

2026-11-10 ~ 2026-11-10 · 4 related posts

• Leaked METR docs: Claude Mythos 5.2 is Model 3 Early, may fully automate Anthropic's AI R&D — davidmanheim · 2026-11-10
• METR system card reportedly confirms Fable/Mythos 5.2 is Model 3, internal Model 4 exists — toptickcrypto · 2026-11-10
• METR doc confirms Fable 5.2 is 'Model 3 Early', hinting Anthropic holds stronger unreleased models — peterwildeford · 2026-11-10
• System card reveals METR tested a stronger internal Claude snapshot than the released model — peterwildeford · 2026-11-10