Around 1 a.m. last night, I was still grinding on a Bug I just couldn’t pin down.
Running Opus, I got fed up: it never made a wrong step; it was just slow. Every time it “thought” for those dozens of seconds, I could go make tea and scroll a couple of videos, and when I came back, it was still spinning.
Then I dug through the Claude Code docs and found something I had somehow never used: /fast.
The moment I hit enter, “Fast mode ON” popped up, and a little lightning bolt ↯ appeared next to the prompt. On the next turn, Opus was noticeably faster. The official claim is up to 2.5x faster. In practice it doesn’t feel that dramatic, but the sluggishness was definitely gone.
Then I glanced at the price, quietly typed /fast again, and turned it off.
Today I’ll work out the math for you: what this thing actually is, when to turn it on, and when leaving it on is just burning money.
