Users Detect Claude Secretly Routing to New Model, Suspected Fable 5.5 Test

Multiple users report that Anthropic appears to be quietly testing a new model, with some Claude Opus 5.5 High requests routed to a mysterious 'Fable 5.5' that performs better, and a simple prompt can reveal whether you're affected.

2026-10-15 ~ 2026-10-15 · 2 related posts

• Users suspect Anthropic is secretly routing Opus 5.5 High requests to a new Fable 5.5 model — 量子位 · 2026-10-15
• Users claim Claude Opus 5.5 is secretly routing to a new, better model — one prompt to check — YashasGunderia · 2026-10-15