The whole hunk
from line 28, old and new numbered
/
lines
from line 28
2828
2929By default, fast mode you turn on in an interactive session persists across sessions. In [non-interactive mode](/docs/en/headless), with the `-p` flag, `/fast` works only in a session launched with fast mode in its [`--settings`](/docs/en/cli-reference#cli-flags) value, for example `claude -p --settings '{"fastMode": true}'`; the toggle then applies to that session only and isn't saved as your default, and in any other non-interactive session the command reports that fast mode isn't available. You can configure fast mode to reset each session. See [require per-session opt-in](#require-per-session-opt-in) for details.
3030
31You can run `/fast` while Claude is working, and Claude Code toggles fast mode without waiting for the turn to end. Claude Code finishes the running turn at its original speed, so the speed change takes effect from your next turn. If your current model doesn't support fast mode, turning it on also switches your model, and Claude Code uses the new model from its next request in that turn.
32
3133For the best cost efficiency, enable fast mode at the start of a session rather than switching mid-conversation. See [understand the cost tradeoff](#understand-the-cost-tradeoff) for details.
3234
3335When you enable fast mode:
3436
35* If you're on a different model, Claude Code automatically switches to Opus
37* If your current model doesn't support fast mode, Claude Code switches to Opus
3638* You'll see a confirmation message: "Fast mode ON"
3739* A small `↯` icon appears next to the prompt while fast mode is active
3840* Run `/fast` again at any time to check whether fast mode is on or off