Effort

Effort sets how much private thinking a model is allowed before it commits to an answer. At higher settings the model writes out a longer chain of intermediate thinking, checks itself, and explores alternatives before producing the visible reply. Those thinking tokens are output tokens, so higher effort costs more money and more wall-clock time per model provider request.

The trade-off is real in both directions. Low effort on a tricky refactor produces confident, fast, wrong code. High effort on 'rename this variable' burns a minute and a pile of tokens for a change that needed none. Much of what people report as 'the model is dumb today' or 'the model is slow today' is an effort setting that doesn't match the task.

Match effort to the job. Planning (in plan mode or on paper), debugging a subtle failure, and anything touching concurrency or security deserve high effort. Mechanical edits, formatting and boilerplate don't. Many harnesses let you flip it per request rather than per session, so the habit is: raise it when you're about to ask something hard, then drop it back down.