Claude Opus 5 only allows disabling thinking at effort high or below
UpdateVerifiedAdded Sep 22, 2026
Disabling thinking with effort xhigh or max returns a 400 error on Claude Opus 5, a breaking change from Opus 4.8 that integrations should check before migrating.
Topics: LLMs
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More Claude Platform releases
Every Claude Platform release| Date | Release | Type |
|---|---|---|
| Jul 24 | Claude Opus 5 launches with a 1M token context window at $5 / $25 per MTok GA | GA |
| Jul 24 | Effort is the primary control for Claude Opus 5 Update | Update |
| Jul 24 | Mid-conversation tool changes enter beta on the Claude API Beta | Beta |
| Jul 24 | Claude API fallbacks parameter adds a default mode for recommended fallbacks Beta | Beta |
| Jul 24 | Fast mode removed for Claude Opus 4.7 Deprecation | Deprecation |
| Jul 22 | Claude Managed Agents agents accept an effort level in model configuration Update | Update |
| Jul 22 | Claude Managed Agents webhooks cover environment and memory store lifecycle Update | Update |
| Jul 22 | Claude Managed Agents sessions can be seeded with initial events Update | Update |
