Claude Code bug leaves Opus 4.8 sessions running without thinking on xhigh WebSearch
sp4mmami · ghdev · 2026-07-21
Bug report: Claude Code fails to enable adaptive thinking on Opus 4.8
A GitHub issue against anthropics/claude-code says the desktop app on Opus 4.8 does not translate alwaysThinkingEnabled: true into thinking: {type: "adaptive"} on outgoing requests.
What breaks
- On Opus 4.8, adaptive thinking is not enabled by default.
- Because the client omits the thinking field, sessions can run silently without extended thinking even when the user expects it.
- At xhigh/max effort, a server-side tool call such as WebSearch fails with:
- outputconfig.effort 'xhigh' is not supported when thinking is disabled on this model
Repro and scope
- Environment: Claude Code Desktop for Windows, Max 5x plan, direct Anthropic connection
- Settings: alwaysThinkingEnabled: true, model: "opus", effortLevel: "medium"
- Switching the same session to Fable 5 works, because adaptive thinking is always on at the API level there
The reporter includes a verified matrix and argues the bug is isolated to client-side request construction for Opus 4.8.
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