Speed Up Opus 4.6 by 2.5x with Fast Mode
When you're in a rapid iteration loop, waiting on Claude is the bottleneck. Fast mode makes Opus 4.6 respond 2.5x faster at the cost of higher token pricing.
Toggle it on with a single command:
/fast
You'll see a ↯ icon next to the prompt when fast mode is active. Run /fast again to check the current state or toggle it off. You can also enable it permanently via settings:
{
"fastMode": true
}
Fast mode isn't a different model. It's the same Opus 4.6 with a different API configuration that prioritises speed over cost efficiency. Quality and capabilities are identical.
A few things worth knowing:
- Enable it at session start for best cost efficiency. Switching mid-conversation charges the full fast mode rate for your entire cached context.
- Combine it with a lower effort level for maximum speed on straightforward tasks:
/fast+--effort low. - Fast mode has its own rate limits, separate from standard Opus 4.6. If you hit them, Claude automatically falls back to standard speed, and the
↯icon turns grey. - It requires extra usage to be enabled on your account and is not available on Bedrock, Vertex AI, or Azure Foundry.
For Teams and Enterprise, an admin must enable it in Claude Code admin settings before users can access it.
Use fast mode for live debugging and rapid iteration; switch back to standard for long autonomous runs where latency doesn't matter.
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When Claude starts referencing files you've since deleted, remembering old code you've already changed, or getting confused by contradictory instructions from a long session — type /clear to wipe the slate clean. Unlike /compact which preserves context, /clear gives you a true fresh start without restarting the CLI.
Not every task needs deep reasoning. Type /fast to switch Claude Code into fast mode — same model, faster output — for quick edits, simple questions, and routine changes. Toggle it off when you need Claude to think harder on complex problems.
Long sessions eat through your context window as conversation history piles up. Type /compact to summarize the conversation so far and reclaim space — keeping Claude's understanding of what you're working on while freeing up room for more work.