Users suspect Anthropic is secretly routing Opus 5.5 High requests to a new Fable 5.5 model
量子位 · wechat · 2026-10-15
Multiple users report that Anthropic appears to be gray-testing a mystery model: requests sent to Opus 5.5 with High thinking may be routed to an unreleased "Fable 5.5" or "Opus 5.6."
Standout demos
- One user produced animated shorts with lighting changes, camera cuts, and sound from minimal prompts—including a Hamilton-style musical using Suno for music, ElevenLabs for vocals, and a synced Three.js video.
- A 30-second "life of a person" sketch animation took just two prompts (four lines), 2 hours, and 27M tokens at Max thinking intensity.
- Other shorts (paper boat, ocean sunset) were rendered entirely by JavaScript code generated in one prompt, no web-sourced assets.
Verification and speculation
- A proposed test: with High thinking on, ask the model to describe VoxelBench or @legitapi without searching—accurate answers suggest you've been routed to the new model.
- Others found little difference vs. regular Opus 5.5.
- Anthropic shipped Opus 5.5, Sonnet 5.5, and Haiku 5.5 within two weeks while Fable sits at 5.1; Opus 5.5 already matches Fable 5.1 on most tasks at 51% lower cost ($4/$20 vs. $10/$50 per million tokens).
Unconfirmed—no official word on which model is actually behind the routing.
Related event: Users Detect Claude Secretly Routing to New Model, Suspected Fable 5.5 Test(2 posts)→
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