Not every task needs the same care. Effort sets how much thinking Claude does before it answers — dial it up for a thorny bug, down for a quick edit. Fast mode is the other dial: it trades a little money for noticeably more speed when you want answers sooner. You set both right in the chat — /effort and /fast work the same in Claude Desktop as in the terminal. On Claude Opus 4.8 the default is already high effort, so the hardest work gets deep thinking without you asking.
Two separate dials control how Claude works, and it’s worth knowing which is
which. Effort is about depth of thought: at higher effort Claude reasons
longer before it acts, which is exactly what you want for a subtle bug or a design
with real trade-offs. Claude Opus 4.8 runs at high effort by default, and
/effort xhigh pushes it further for the hardest tasks. Lower effort is fine — and
faster — for small, obvious edits.
Fast mode is a different trade entirely: it doesn’t change how carefully Claude
thinks, it changes how quickly it responds. Toggle it with /fast to get roughly
2.5× the speed for a higher per-token rate — handy when you’re iterating in tight
loops and waiting is the bottleneck. Turn it back off when you’re done and want the
standard rate again.
The rule of thumb: use effort to match the difficulty of the task, and fast
mode to match your impatience. They stack — you can run a hard task at high effort
and in fast mode if both depth and speed matter. You set both by typing /effort
and /fast in the chat, the same in Claude Desktop as in the terminal.
why it helps Spend the model's effort where it pays off — and get speed when you're in a hurry.
examples- Reach for
/effort xhighon the genuinely hard stuff — a subtle bug, a tricky design — and leave it on high for everyday work. - Turn on
/fastwhen you're iterating quickly and want answers sooner; it costs a bit more per token for the extra speed. - Higher effort means Claude thinks longer before acting — great for correctness, slower for trivial edits.
Questions people ask
- What's the difference between effort and fast mode?
- Effort sets how *hard* Claude thinks before answering — dial it up for a thorny bug, down for a quick edit. Fast mode sets how *fast* it responds, trading a bit more cost for roughly 2.5× the speed. One is depth; the other is speed.
- Do I need to turn on high effort myself?
- Not for most work — Claude Opus 4.8 runs at high effort by default, so the hardest tasks already get deep thinking. Use `/effort xhigh` to push it further on the genuinely hard stuff.
- Does fast mode use a weaker model?
- No. Fast mode doesn't change how carefully Claude thinks — it only changes how quickly it responds, for a higher per-token rate. Turn it back off with `/fast` when you want the standard rate again.
- Can I use high effort and fast mode at the same time?
- Yes — they stack. Run a hard task at high effort *and* in fast mode when both depth and speed matter.
- Do effort and fast mode work in Claude Desktop?
- Yes. You set both by typing `/effort` and `/fast` in the Desktop chat, exactly as in the terminal — they're chat settings, not command-line-only features.