Opus 5.5 has 5 effort levels. Most people only ever use one.
Effort controls how hard Claude thinks on each request. Here's when to use each 👇
→ Low: when the plan is clear. Renames, or applying a known pattern across files
→ Medium: your starting point for well-scoped daily work
→ High: when medium stalls. More thinking per turn catches what medium misses
→ Extra high: when high still can't get there. Still stuck? Switch to Fable 5.1 for that task
→ Max: for the most complex tasks only. Turn it on, finish the hard part, then lower it again
Not getting the results you expected? Raise the effort before you switch to a bigger model.