Remember ultrathink? The magic keyword that unlocked Claude’s maximum reasoning power? It’s deprecated. But here’s what replaced it — and a hidden trick to get twice the thinking budget on 64K output models. The Old Way: The ultrathink Keyword For months, ultrathink was the magic word. Add it to your prompt, get 31,999 thinking tokens. Hacker News threads debated its effectiveness. Power users swore by the “Opus + Ultrathink + Plan Mode” combo. Under the hood, Claude Code detected the keyword and set the thinking budget: // Simplified (other keywords like "megathink" and "think" existed too) const thinkingBudget = prompt.includes("ultrathink") ? 31999 : 0; // Passed to the Anthropic API await client.messages.create({ model: "claude-sonnet-4-...", messages: [...], thinking: thinkingBudget > 0 ? { type: "enabled", budget_tokens: thinkingBudget // ← This is what matters } : undefined }); What Changed On January 16, 2026, Anthropic closed the book on ultrathink: “Closing as ultrathink is now deprecated and thinking mode is enabled by default.” — Sarah Deaton, Anthropic If you type “ultrathink” now, you’ll see this message: The New Default Extended thinking is now automatically enabled for supported models: Opus 4.5 ✓ Sonnet 4.5 ✓ Sonnet 4 ✓ Haiku 4.5 ✓ Opus 4 ✓ Claude 3.x ✗ (not supported) The default budget? 31,999 tokens — the same as the old ultrathink maximum. Here’s what happens now on every API call: // 1. Determine thinking budget let budgetTokens = 31999; // Default: max if (process.env.MAX_THINKING_TOKENS) { budgetTokens = parseInt(process.env.MAX_THINKING_TOKENS); } // 2. Auto-enabled for supported models const thinkingEnabled = isSupportedModel(model); // Opus 4.5, Sonnet 4/4.5, Haiku 4.5, Opus 4 // 3. Passed to Anthropic API on every request await client.messages.create({ model: "claude-sonnet-4-...", messages: [...], thinking: thinkingEnabled ? { type: "enabled", budget_tokens: budgetTokens // ← 31,999 by default } : undefined }); Translation: You no longer...
First seen: 2026-01-19 05:29
Last seen: 2026-01-19 05:29