Post #4272013

> Claude Opus 5 runs with thinking on by default, and thinking can be disabled only at effort high or below; see the migration guide. With thinking disabled, two artifacts can occasionally appear in the model's visible output. The primary mitigation for both is to keep thinking enabled and control token cost with lower effort levels instead of disabling thinking: for most tasks, thinking enabled at low effort performs better than thinking disabled at similar cost. https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5