What is "Ultrathink" in Claude Code?

"Ultrathink" in Claude Code is a special command word or "magic word" that you can include in your prompt when using Claude Code, Anthropic's agentic coding tool (typically accessed via command-line interface). When you add "ultrathink" to your request, it automatically triggers the system to allocate the maximum thinking budget—the highest level of computational resources—for complex problem solving and deep analysis.

How Ultrathink Works

• Keyword Trigger: Including "ultrathink" (or similar phrases like "think really hard") signals Claude Code to switch into its deepest analytical mode.
• Token Budget: This triggers a fixed allocation of around 31,999 tokens, allowing the AI to spend more time evaluating alternatives, considering edge cases, and producing more thorough solutions than standard or even "think" or "megathink" modes (which typically allocate 4,000 or 10,000 tokens, respectively)^[1][2][3].
• Scope: Ultrathink only works in Claude Code's CLI environment. It does not work in the standard web chat or API interfaces^[3][4].
• Intended Use: It's designed for the most challenging coding, architectural, or optimization tasks where deep analysis is crucial. Due to the high token (and therefore cost and time) consumption, it's recommended for situations where exceptional solution quality justifies the expense^[3][1].

Example Usage

You simply append "ultrathink" to your prompt, like:

Plan the implementation strategy for this complex feature ultrathink

Analyze the codebase and recommend optimization opportunities ultrathink

Thinking Levels in Claude Code

Claude Code recognizes several levels:

Best Practices

• Do not use ultrathink by default. Reserve it for the most involved problems, as frequent use can quickly deplete your available tokens or credits^[5][3].
• Strategically escalate. Start with "think" or "megathink" and only use "ultrathink" if necessary for especially complex challenges^[1].

In summary, "ultrathink" is a powerful built-in feature in Claude Code for unlocking maximum reasoning depth—useful for advanced engineering work where the quality of analysis outweighs the computational cost^[2][3][5].