Ultrathink | ClaudeLog

Maximize test-time compute with ultrathink and revving mechanics to push Sonnet to its limits.

Ultrathink Unlock Claude's maximum reasoning power by adding "ultrathink" to your prompts. Re-introduced in v2.1.68, "ultrathink" triggers high effort mode for the next turn—combined with Plan Mode, it can push Sonnet to near-Opus performance on complex tasks. Ultrathink & Plan Mode​ I personally get outstanding results using ultrathink + Plan Mode with Claude Sonnet 4.5. This combination is especially useful when you don't want to reach for Claude 4 Opus. I have found it can often bridge the intelligence gap for complex tasks, and when that's not sufficient, I opt to rev the model by…

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