Dispatch (Cowork Beta) forces unavailable Claude Fable 5, ignoring account default model → all dispatched tasks fail
Summary: In Cowork → Dispatch (Beta), the model is server-assigned to claude-fable-5[1m] regardless of the account's selected default model. Because Claude Fable 5 is currently unavailable, every dispatched message returns "Claude Fable 5 is currently unavailable" and no task can run. Regular Cowork correctly uses my selected Opus 4.8 — only Dispatch is affected. There is no model selector in Dispatch, so there is no user-facing way to change it.
Environment
- Claude desktop app (macOS)
- Cowork → Dispatch (Beta)
- Max plan
- Account default model: Opus 4.8 (confirmed selected in the Cowork model picker)
Steps to reproduce
- Set/confirm account default model = Opus 4.8 (blue check in the Cowork model picker).
- Open Dispatch and send any message (e.g. "what model are you using").
- Every reply is: "Claude Fable 5 is currently unavailable. Learn more: https://www.anthropic.com/news/fable-mythos-access"*
Expected: Dispatch uses my selected default (Opus 4.8), or at minimum falls back to an available model.
Actual: Dispatch is pinned to the unavailable Fable 5; all dispatched tasks are blocked.
Diagnosis / evidence
The Cowork client cache cowork-clientdata-cache.json contains:
{"clientDataCache":{},"cwkCfgKeyForModel":{"apiModel":"claude-fable-5[1m]","cwkCfgKey":"marigold"}}<img width="838" height="1670" alt="Image" src="https://github.com/user-attachments/assets/ebfb404a-ca75-42ac-b5df-d573a8af8c13" />
I ruled out every client-side cause:
- Cleared this cache (set
cwkCfgKeyForModelto{}) and relaunched → app re-fetched and rewrote the identicalclaude-fable-5[1m]/"marigold"value. - Full sign-out / sign-in on both desktop and phone → identical value returned again.
- Account default model is Opus 4.8 and is respected everywhere except Dispatch.
- No env var or local config pins the model.
This confirms the Fable 5 assignment for Dispatch is server-side, bound to the account, and cannot be changed by the user. Since Fable 5 is currently unavailable, Dispatch is completely unusable.
Impact: Dispatch is 100% blocked for affected accounts — no task can be dispatched at all.
Suggested fixes
- Have Dispatch honor the account's selected default model, and/or
- Fall back to an available model (e.g. Opus 4.8) when the assigned model is unavailable.//
Related: #43956 (no model/product selector for Dispatch)