Type /effort in Claude Code. Claude Academy puts it simply: effort tells your model how many resources to spend on a task, and it does not change what the model knows.
What each level is for
Low and Medium: routine work. Most tasks should run here, and your usage goes further.
High: the best balance for bigger jobs.
Extra high: long coding tasks.
Max: really hard questions or problems.
Ultracode: runs at extra high and, on big tasks, splits the work across multiple agents. Powerful, and it burns through your usage fastest.
Auto: Claude decides for each request.
The test
Run the exact same routine task on Low and on Ultracode, then compare the result and the usage. For most things the difference in the result is small, and the difference in usage isn't.
A simple rule
Start low. Move up only when the answer isn't good enough, and come back down when the hard part's done.
Your default is High on Team, Enterprise and API plans, and Medium on the others.