Claude Code Fast Mode: 2.5x Faster Opus 4.6 Responses

Problem: You're iterating on code with Opus 4.6 and the response times feel sluggish for interactive work. Reducing the effort level trades quality for speed. You want full Opus 4.6 reasoning at a faster pace.

Quick Win: Type /fast in your Claude Code session and press Tab to toggle fast mode on. You'll see a lightning bolt icon next to your prompt. Same model, 2.5x faster output.

What Fast Mode Actually Is

Here's the most important thing to understand about Claude Code fast mode: it does not switch you to a different model. You're still running Claude Opus 4.6. The same weights, the same capabilities, the same quality ceiling. This isn't Haiku wearing an Opus label. It's actual Opus 4.6 with infrastructure-level priority.

What changes is the API configuration behind the scenes. Anthropic routes your requests through a faster serving path, delivering responses roughly 2.5x faster than standard Opus 4.6. You pay more per token for this priority treatment, but the intelligence stays identical. The model doesn't skip reasoning steps or compress its output to hit lower latency. It produces the same response, just faster.

This distinction matters because the traditional path to faster Claude Code responses has been reducing your effort level, which genuinely reduces thinking depth. A lower effort level tells the model to spend less time reasoning, which works for simple tasks but hurts quality on anything complex. Fast mode sidesteps that tradeoff entirely. You get speed without sacrificing quality.

Fast mode launched as a research preview, so expect Anthropic to refine pricing, rate limits, and the overall experience over time.

How to Enable Claude Code Fast Mode

Toggle fast mode with a single command:

/fast

Press Tab to confirm. That's it. A lightning bolt icon appears next to your prompt, confirming fast mode is active. Run /fast again to disable it.

You can also set it permanently in your user settings file:

{
  "fastMode": true
}

See the settings reference for all available configuration options.

A few behaviors to know:

• Persists across sessions. Once enabled, fast mode stays on until you disable it.
• Auto-switches to Opus 4.6. If you're on Haiku or Sonnet when you enable fast mode, it bumps you to Opus 4.6 automatically.
• Disabling keeps your model. When you toggle fast mode off with /fast, you stay on Opus 4.6. Use /model to switch to a different model if needed.

Pricing Breakdown

Opus 4.6 fast mode pricing varies based on your context window size. Here's the full pricing table:

Several pricing details matter for budgeting:

• Compatible with 1M extended context. Fast mode works with the full 1M context window, though pricing increases above 200K tokens.
• Billed to extra usage only. Fast mode tokens don't count against your plan's included usage. Every token goes straight to extra usage billing.
• Switching mid-conversation is expensive. When you enable fast mode partway through a session, you pay the full uncached input price for your entire existing context. Enable fast mode at the start of a session for the best cost efficiency.

When to Use Fast Mode

Fast mode shines during interactive work where latency directly impacts your productivity:

• Rapid iteration cycles. You make a change, test it, ask Claude to adjust, and repeat. The 2.5x speed boost compounds across dozens of these micro-interactions per session. In a typical debugging session with 25 back-and-forth exchanges, fast mode shaves roughly 15-20 minutes off the total wait time compared to standard Opus 4.6. A task that involves 20 round-trips feels fundamentally different at 2.5x speed.
• Live debugging. When you're chasing a bug through stack traces and log output, waiting for responses breaks your concentration. Faster answers keep you in flow state. You stay locked onto the problem instead of losing your mental thread while waiting.
• Time-sensitive deadlines. Shipping a fix at 2 AM or racing to complete a feature before a demo. Those are the moments where paying extra per token makes obvious sense. The cost premium disappears when measured against the value of shipping faster.
• Interactive pair programming. When latency matters more than cost, because you're actively thinking alongside Claude and every pause disrupts the rhythm. This is especially true during design discussions where you're bouncing ideas back and forth rapidly.

When to Skip Fast Mode

Standard Opus 4.6 is the better choice when speed isn't the bottleneck. The simple test: will you be actively waiting for the response? If not, standard mode gives you the same output at a lower cost.

• Long autonomous tasks. If you're kicking off a large refactor and walking away, the response time doesn't affect your workflow. Save the money.
• Batch processing or CI/CD pipelines. Automated workflows don't benefit from lower latency. Standard rates make more sense here.
• Cost-sensitive workloads. When you're burning through tokens on a large codebase analysis, standard mode delivers the same results at a lower rate. The output quality is identical, so there's no reason to pay the premium.
• Tasks where you step away. If you tell Claude to restructure an entire module and go grab coffee, you won't notice the speed difference. Fast mode only matters when you're sitting there watching the cursor.

Fast Mode vs. Effort Level

These two settings affect speed through completely different mechanisms:

You can combine both. Running fast mode with a reduced effort level stacks the 2.5x infrastructure speed with less thinking overhead. This combination works well for straightforward tasks like formatting, simple refactors, or generating boilerplate where efficiency patterns matter more than deep analysis. For complex architectural decisions or tricky debugging, keep the effort level high and let fast mode handle the speed. The two settings give you independent control over quality and latency, which means you can optimize for each task individually rather than settling for a single compromise.

For a deeper look at how effort levels affect output quality, see our guide on deep thinking techniques.

Rate Limits and Fallback Behavior

Fast mode has its own rate limits, separate from standard Opus 4.6. This means enabling fast mode doesn't eat into your standard Opus 4.6 rate limit, and vice versa. When you hit the fast mode ceiling, Claude Code handles it gracefully:

1. Auto-fallback to standard Opus 4.6. Your session continues without interruption. You just lose the speed boost temporarily. No error messages, no broken workflow.
2. Lightning bolt turns gray. The icon changes to a cooldown indicator, so you always know which mode is active at a glance.
3. Standard speed and pricing apply. During fallback, you're billed at normal Opus 4.6 rates. This is actually a nice cost break if you've been running fast mode heavily.
4. Auto re-enables when ready. Once your rate limit cooldown expires, fast mode kicks back in automatically. No action needed on your end.

If you'd rather not wait for the cooldown, run /fast to disable fast mode manually and continue at standard rates indefinitely.

Requirements and Availability

Fast mode isn't available everywhere. Here's what you need:

• Anthropic direct only. Fast mode works through the Anthropic Console API and Claude subscription plans. It's not available on Amazon Bedrock, Google Vertex AI, or Microsoft Azure Foundry.
• Extra usage must be enabled. Since fast mode bills entirely to extra usage, your account needs extra usage turned on.
• Teams and Enterprise restrictions. Organization admins must explicitly enable fast mode in Console settings or Claude AI admin settings. If your admin hasn't enabled it, running /fast returns: "Fast mode has been disabled by your organization."

Fast Mode with Agent Teams

When running agent teams, fast mode applies to the lead session only. Your teammate agents can use different speed configurations independently. This gives you granular control over cost allocation across a multi-agent workflow.

A practical approach for team-based workflows: enable fast mode on the lead agent for quick coordination and decision-making, while teammates run at standard speed to keep costs manageable. The lead agent typically handles shorter, more interactive exchanges where latency matters most, like reviewing teammate output, making routing decisions, and responding to your direct questions. Teammates handle longer, autonomous tasks like writing tests, refactoring modules, or generating documentation, where the 2.5x speed boost wouldn't noticeably change your experience.

Cost Optimization Tips

A few practical ways to keep fast mode costs under control:

• Enable at session start. Switching to fast mode mid-conversation forces a full-context re-price at the uncached input rate. If your context window already holds 50K tokens, that's a real hit. Starting with fast mode from the first message avoids this penalty entirely.
• Pair with effort levels. Use fast mode plus a lower effort level for simple tasks, then bump effort back up for complex work. This gives you maximum speed when quality requirements are lower.
• Toggle based on work type. Use fast mode during active coding sessions, then disable it before kicking off autonomous work. Five seconds of toggling can save meaningful token costs over a full day of development.
• Monitor through Console. Check your usage and billing in the Anthropic Console dashboard to track how fast mode affects your spend. Watching your usage patterns for a week or two will help you find the right balance between speed and cost for your workflow.

Putting It Together

Fast mode fills a specific gap: you want Opus 4.6 quality without Opus 4.6 latency. The tradeoff is cost, not capability. For developers who spend hours per day in interactive Claude Code sessions, that tradeoff pays for itself through sustained focus and faster iteration cycles.

Think of it this way: Claude Code now gives you three independent levers for tuning performance. Fast mode controls infrastructure speed. Effort levels control thinking depth. And model selection controls the base capability tier. Each lever operates independently, and you can combine them in whatever way fits your current task.

For your highest-value interactive work, turn everything up: fast mode on, high effort, Opus 4.6. For quick formatting or boilerplate, try fast mode with low effort. For background tasks you won't watch, standard speed saves money without any perceived cost. The key is matching each setting to the work in front of you, not picking one configuration and leaving it forever.

If you want this kind of model routing handled for you, ClaudeFast's Code Kit includes a pre-configured 5-tier complexity system that automatically matches model selection and thinking depth to each task -- so trivial fixes get fast responses while architectural decisions get full Opus reasoning.