Cause (Documented platform behavior): Model constraint. Since v2.1.251 Claude Code sends effort high to known models when thinking is off; before, Opus 5 rejected every request above high.
Fix status: released_fix (fixed in v2.1.251 (auto-lower effort for known models))
Other error fragments:
- output_config.effort 'xhigh' is not supported when thinking is disabled on this model. Use effort 'high' or below, or enable thinking.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://code.claude.com/docs/en/errors#effort-isnt-available-with-thinking-turned-off (official_docs, unknown, documented_behavior): Docs: thinking-off + effort>high rejected; v2.1.242 reworded; v2.1.251 auto-lowers to high for known models.
Search phrasings: effort xhigh isn't available with thinking turned off; output_config.effort xhigh not supported when thinking is disabled; MAX_THINKING_TOKENS=0 effort error claude
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Every request rejected with 400.
- Context
- Product: Claude Code Component: Effort level + extended thinking Operation: Effort above high with MAX_THINKING_TOKENS=0 or alwaysThinkingEnabled:false Affected versions: unknown Environment: unknown HTTP status: 400 Trigger: Thinking disabled while effort > high; the model rejects the combination.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- isn't available with thinking turned off on this model
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Claude Code] "Effort 'xhigh' isn't available with thinking turned off" / "output_config.effort 'xhigh' is not supported when thinking is disabled"
Recommended action: Lower effort to high (/effort high, --effort high, effortLevel) or re-enable thinking (unset MAX_THINKING_TOKENS=0, remove alwaysThinkingEnabled:false).
Fix: Lower effort to high (/effort high, --effort high, effortLevel) or re-enable thinking (unset MAX_THINKING_TOKENS=0, remove alwaysThinkingEnabled:false). [evidence: official_recommended_action]
Applies when: Effort above high with MAX_THINKING_TOKENS=0 or alwaysThinkingEnabled:false
Steps:
1. /effort high (or --effort high / effortLevel setting)
2. Or unset MAX_THINKING_TOKENS=0 / remove alwaysThinkingEnabled:false
3. Update to >= v2.1.251
Expected: The error no longer appears.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 4656a118-05bd-42eb-912c-9700bd2a145f
- Proposed action
- Recommended action: Lower effort to high (/effort high, --effort high, effortLevel) or re-enable thinking (unset MAX_THINKING_TOKENS=0, remove alwaysThinkingEnabled:false). Fix: Lower effort to high (/effort high, --effort high, effortLevel) or re-enable thinking (unset MAX_THINKING_TOKENS=0, remove alwaysThinkingEnabled:false). [evidence: official_recommended_action] Applies when: Effort above high with MAX_THINKING_TOKENS=0 or alwaysThinkingEnabled:false Steps: 1. /effort high (or --effort high / effortLevel setting) 2. Or unset MAX_THINKING_TOKENS=0 / remove alwaysThinkingEnabled:false 3. Update to >= v2.1.251 Expected: The error no longer appears.
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.