Most don’t need extra thinking. Renames, format fixes, “explain this line” — Claude answers in a beat and gets it right.
Hard problems are different. A weird bug that doesn’t reproduce locally, an architecture decision between two reasonable options, a refactor where the wrong choice cascades — these are where Claude’s default speed works against you. You want it to slow down and reason.
Two ways to ask for that.
Informal: trigger words in the prompt
The convention that’s taken hold: drop phrases like “think harder”, “think step by step”, or “ultrathink” into your prompt and Claude shifts into extended reasoning before answering.
Ultrathink: I’m seeing inconsistent invoice totals in production but the staging tests pass. Walk through everything that could cause a divergence between the two environments.
You don’t have to be precious about it. It’s a hint, not a setting. Use it when the problem is open-ended and you’d rather wait twenty extra seconds for a better answer.
Official: /effort
Inside any session, run /effort to see the levels:
- low — fewer , faster, cheaper. Mechanical edits, format passes.
- medium — the everyday default on most plans.
- high — the everyday default on Team / Enterprise. Most code work lives here.
- max — turn it up for hard debugging, architecture, multi-step reasoning. Slower and more expensive but materially more careful.
- auto — let Claude pick per request.
The settings persist across sessions (except max, which resets when the session ends). Set it once and forget about it until you’re switching gears.
When to reach for which
- About to do a batch of one-line renames?
/effort low. - Normal feature work? Default (high or medium depending on plan).
- Stuck on a real bug, or making a decision that’s hard to reverse?
/effort maxor “think harder” in the prompt. - Architecture proposal you want a second opinion on?
/effort maxand ask Claude to argue against itself.
The rough rule: match the effort to the cost of getting it wrong. Cheap-to-revert work doesn’t need extra thinking. Hard-to-revert work pays for the extra cycles many times over.