Claude Opus 5 defaults reasoning on and can reject xhigh or max without it
rohanpaul_ai · x · 2026-07-25
One migration trap with Claude Opus 5: thinking is now on by default, and trying to disable it while selecting xhigh or max returns an API error.
The post also says Opus 5 tends to:
- produce longer deliverables
- narrate agent progress more frequently
- delegate to subagents more readily than Opus 4.8
So beyond raw benchmark claims, the practical change is that the model behaves more like a deeply agentic system and may require code or workflow adjustments during migration.
Related event: Claude Opus 5 Introduces Five Effort Levels with Default Reasoning(2 posts)→
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