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Fast mode for Claude Opus 5.5 is available, and fast mode for Claude Opus 5 and Claude Opus 4.8 is in research preview.
Fast mode is a high-speed configuration for Claude Opus, making the model up to 2.5x faster at a higher cost per token. Toggle it on with /fast when you need speed for interactive work like rapid iteration or live debugging, and toggle it off when cost matters more than latency. Fast mode is not a different model. It uses Claude Opus with a different API configuration that prioritizes speed over cost efficiency. You get identical quality and capabilities with faster responses. Fast mode is supported on Opus 5.5, Opus 5, and Opus 4.8. It is not available on Sonnet, Haiku, or other models.
Fast mode for Opus 4.8 was deprecated on October 30, 2026, and will be removed on November 30, 2026. If Opus 4.8 is still your model with fast mode on after that date, the API rejects your requests. By that date, switch to Opus 5.5 or turn fast mode off in your session:
Opus 4.7 doesn’t support fast mode, so switching to it turns fast mode off. Fast mode for Opus 4.7 was deprecated on June 25, 2026, and removed on July 24, 2026. What to know:
  • Use /fast to toggle on fast mode in the Claude Code CLI. The VS Code extension offers a Toggle fast mode command when the selected model supports fast mode. Claude Code saves that toggle to your fastMode setting.
  • Fast mode pricing per MTok input/output is $8/$40 on Opus 5.5 and $10/$50 on Opus 5 and Opus 4.8.
  • Available to Claude Code users on subscription plans (Pro/Max/Ultra/Team/Enterprise) and on Claude Console. Team and Enterprise organizations need an Owner to enable it first, and Console organizations need access provisioned first to use it with Opus 5 or Opus 4.8. Requirements describes both.
  • For Claude Code users on subscription plans (Pro/Max/Ultra/Team/Enterprise), fast mode is available via usage credits only and not included in the subscription rate limits.

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Toggle fast mode

In the CLI, toggle fast mode in either of these ways:
  • Run /fast, press Space to toggle on or off, then press Enter to confirm
  • On a model that supports fast mode, set "fastMode": true in your user settings file. If you set it on any other model, you stay on that model with fast mode off.
By default, fast mode you turn on in an interactive session persists across sessions on a supported model. You can configure fast mode to reset each session. See require per-session opt-in for details. Outside a cloud session, in non-interactive mode with the -p flag, /fast works only in a session launched with fast mode in its --settings value, for example claude -p --settings '{"fastMode": true}'; the toggle then applies to that session only and isn’t saved as your default. The -p form requires Claude Code v2.1.205 or later. Elsewhere in non-interactive mode, the command reports that fast mode isn’t available. You 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. For the best cost efficiency, enable fast mode at the start of a session rather than switching mid-conversation. See understand the cost tradeoff for details. When you enable fast mode with /fast:
  • If your current model doesn’t support fast mode, Claude Code switches to Opus
  • You’ll see a confirmation message: “Fast mode ON”
  • A small ↯ icon appears next to the prompt while fast mode is active
  • Run /fast again at any time to check whether fast mode is on or off
Opus 5.5 is the fast mode default in Claude Code v2.1.280 and later. Before v2.1.280, fast mode defaulted to Opus 5 from v2.1.219. When you disable fast mode with /fast again, you remain on Opus. To switch to a different model, use /model.

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Switch models while fast mode is on

Fast mode follows your model switches in both directions:
  • Switch away: when you switch to a model that doesn’t support fast mode, Claude Code turns fast mode off. This includes Opus 4.7; before v2.1.221, fast mode stayed on after a switch to Opus 4.7 and the API rejected the requests.
  • Switch back: switching back to a supported Opus model turns fast mode on again when your saved fast mode preference is on, the same preference a new session starts from by default. A model switch never turns fast mode on for a session whose saved preference is off, and with per-session opt-in configured, switching back doesn’t turn it on either; run /fast to re-enable it.
Whenever a model switch turns fast mode on or off, Claude Code shows a Fast mode ON or Fast mode OFF confirmation, and the ↯ icon appears while fast mode is on. This holds whether you switch with /model, with /config model=<model>, or from a device connected through Remote Control. Claude Code resends the session’s fast mode status to devices connected through Remote Control after a model switch, a reconnection, or a failed availability check.

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Use fast mode in cloud sessions

Fast mode works in cloud sessions when it’s available on your account, whether the session runs on Anthropic-managed infrastructure or a self-hosted runner. Requires Claude Code v2.1.271 or later in the session’s environment. Type /fast on in the session to turn fast mode on. It stays on for that session only and isn’t saved as your default. The requirements apply in cloud sessions too. In the browser at claude.ai/code, you can also turn fast mode on and off from the model menu on the message box. The menu shows the switch when your plan includes fast mode and the selected model supports it.

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Understand the cost tradeoff

Fast mode has higher per-token pricing than standard Opus: Fast mode pricing is flat across the full 1M token context window. For the standard Opus rate to compare against, see the Claude pricing reference. The first time you enable fast mode in a conversation, you pay the full fast mode uncached input token price for the entire conversation context. The deeper into a conversation you are, the more this costs, so the charge is smallest when you enable fast mode at the start. Fast mode and standard speed keep separate caches, so each later switch reads part or all of the conversation uncached again.

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See where fast mode spend appears

You see fast mode spend in a different place depending on how you signed in, so first run /status to check. If it shows a Login method row such as Claude Max account, you signed in with a Claude subscription. If it shows an API key row instead, your requests bill to a Claude Console organization.
  • Pro, Max, and Ultra: you pay for fast mode from your usage credits. Go to Settings > Usage on claude.ai, where the Usage credits section shows how much you’ve spent in usage credits this month. That figure includes fast mode but doesn’t break it out separately.
  • Team and Enterprise: your organization pays for your fast mode usage from its usage credits. To see your own usage-credits spend, run /usage. For where your organization sees that spend, see Claude for Teams and Enterprise.
  • Claude Console: your organization pays for fast mode with the rest of its API usage. On the Console Usage and Cost pages, select Speed (research preview) in the Group by menu to separate fast mode from standard-speed usage. You see that option only when the selected date range includes fast mode usage.

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Decide when to use fast mode

Fast mode is best for interactive work where response latency matters more than cost:
  • Rapid iteration on code changes
  • Live debugging sessions
  • Time-sensitive work with tight deadlines
Standard mode is better for:
  • Long autonomous tasks where speed matters less
  • Batch processing or CI/CD pipelines
  • Cost-sensitive workloads

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Fast mode vs effort level

Fast mode and effort level both affect response speed, but differently: You can combine both: use fast mode with a lower effort level for maximum speed on straightforward tasks.

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Requirements

Fast mode requires all of the following:
  • Anthropic API or subscription only: fast mode is available through the Anthropic Console API and for Claude subscription plans using usage credits. It is not available on Amazon Bedrock, Google Cloud’s Agent Platform, Microsoft Foundry, or Claude Platform on AWS. Console organizations must also have fast mode access provisioned to use it with Opus 5 or Opus 4.8.
  • Usage credits turned on for subscription plans: on a Pro, Max, Ultra, Team, or Enterprise plan, your account must have usage credits turned on, which allows billing beyond your plan’s included usage. Until they’re on, /fast reports “Fast mode requires usage credits”. To turn them on, follow the step for your plan:
    • On Pro, Max, and Ultra, turn them on in the Usage credits section of Settings > Usage on claude.ai, or run /usage-credits to open that page.
    • On Team and Enterprise, a member with billing access turns them on for the organization at Organization settings > Usage, and a member without it runs /usage-credits to send the organization’s admins a request.
Fast mode usage draws directly from usage credits, even if you have remaining usage on your plan.
  • Paid Console organization: Claude Console accounts don’t use usage credits, and your organization pays for fast mode per token with the rest of its API usage. On the Console’s free Evaluation plan, /fast shows “Fast mode unavailable during evaluation. Please purchase credits.” To clear it, purchase credits in your Console billing settings. Fast mode with Opus 5.5 also depends on your organization’s usage tier.
  • Owner enablement for Team and Enterprise: fast mode is disabled by default for Team and Enterprise organizations. An Owner must explicitly enable fast mode before users can access it.
Four organization settings can block turning fast mode on with /fast:
  • Fast mode not enabled: if fast mode hasn’t been enabled for your organization, turning fast mode on with /fast shows “Fast mode has been disabled by your organization.”
  • Fast mode turned off by managed settings: if your organization deploys managed settings that set fastMode: false, turning fast mode on with /fast shows the same “Fast mode has been disabled by your organization” message.
  • Per-session opt-in required: managed settings that set fastModePerSessionOptIn: true refuse /fast on with the same message everywhere except an interactive terminal session.
  • Fast-mode model not allowed: if your organization’s availableModels allowlist excludes the fast-mode Opus model, turning it on is refused with “is not in your organization’s allowed models”. In a session already running on an allowed Opus model that supports fast mode, /fast instead enables fast mode on your current model without switching models.

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Enable fast mode for your organization

Where you enable fast mode depends on which product your organization uses: Console organizations that use Claude Opus 5 or Claude Opus 4.8 also need provisioned access, as described in fast mode on the Claude API. Without that access, fast mode requests on those models hit the fast mode rate limit and fall back to standard speed until access is provisioned. Another option to disable fast mode entirely is to set CLAUDE_CODE_DISABLE_FAST_MODE=1. See Environment variables.

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Use fast mode behind proxies and LLM gateways

Before offering fast mode, Claude Code checks your organization’s fast mode availability with a request directly to api.anthropic.com. The check doesn’t follow ANTHROPIC_BASE_URL, so on a network that routes Claude traffic through an LLM gateway and blocks direct egress to api.anthropic.com, the check fails even though inference requests work. The check does use a configured HTTP proxy, so a network block fails the check only where api.anthropic.com is unreachable even through the proxy. If your organization has fast mode enabled and /fast says otherwise, find the message it shows among these cases.

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Fast mode unavailable due to network connectivity issues

The availability check failed, for example because your network blocks api.anthropic.com, and requests run at standard speed. A check that succeeded in the past keeps working from its cached result, so a blocked check mostly affects new installations. To restore fast mode, allowlist direct egress to api.anthropic.com, or set CLAUDE_CODE_SKIP_FAST_MODE_NETWORK_ERRORS=1, which treats a failed check as available and still honors a “disabled by your organization” response.

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Fast mode is currently unavailable

Behind a gateway, check for these configurations, in which Claude Code doesn’t send the availability check and has no earlier successful check cached: To restore fast mode in either configuration, set CLAUDE_CODE_SKIP_FAST_MODE_NETWORK_ERRORS=1.

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Fast mode has been disabled by your organization

Behind a gateway, you can see this message even when your organization has fast mode enabled, in either of these configurations:
  • You authenticate with ANTHROPIC_AUTH_TOKEN alone, with no claude.ai login, no API key, and no cached successful check. Claude Code then treats fast mode as disabled by your organization without sending the request.
  • A proxy intercepts the check and answers with its own page, for example a TLS-inspecting proxy returning an HTTP 200 block page. Claude Code reads that page as a response saying your organization has fast mode disabled.
In both cases, set CLAUDE_CODE_SKIP_FAST_MODE_ORG_CHECK=1, which skips the check entirely, rather than CLAUDE_CODE_SKIP_FAST_MODE_NETWORK_ERRORS, which doesn’t apply to either.
The skip variables change only the client-side check. When your organization has fast mode disabled, the API rejects fast mode requests whether or not they’re set. Claude Code then retries the request at standard speed, turns fast mode off, and /fast reports that your organization has disabled fast mode.

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Require per-session opt-in

By default, fast mode a user turns on in an interactive session persists across sessions on a supported model. To change this, set fastModePerSessionOptIn to true in any settings file, which causes each session to start with fast mode off and requires users to explicitly enable it with /fast. Owners on Team or Enterprise plans can deploy it organization-wide through server-managed settings.
This is useful for controlling costs in organizations where users run multiple concurrent sessions. The user’s fast mode preference is still saved, so removing this setting restores the default persistent behavior. When managed settings set the key, /fast on works only in an interactive terminal session. Everywhere else, including non-interactive mode, the VS Code extension, and cloud sessions, it’s refused with a message that your organization has disabled fast mode.

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Handle rate limits

Fast mode has separate rate limits from standard Opus; for Console organizations, the Claude Platform’s rate limits page describes them. When you hit the fast mode rate limit:
  1. Fast mode automatically falls back to standard speed
  2. The ↯ icon turns gray to indicate cooldown
  3. You continue working at standard speed and pricing
  4. When the cooldown expires, fast mode automatically re-enables
To disable fast mode manually instead of waiting for cooldown, run /fast again. If you run out of usage credits mid-session, Claude Code retries each rejected fast mode request at standard speed and pricing, so you keep working, and there is no cooldown. How you see the rejection depends on the session type:
  • In an interactive session, Claude Code shows a “Fast mode disabled · Out of usage credits” notification and turns fast mode off. Your saved fast mode preference doesn’t change; run /fast to turn fast mode back on.
  • In non-interactive mode with --output-format stream-json, and through the Agent SDK, Claude Code emits the same text on the message stream as a system message with subtype notification, once per turn while you’re out of usage credits. Fast mode stays on. Requires Claude Code v2.1.221 or later.

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Research preview

Fast mode for Claude Opus 5 and Claude Opus 4.8 is a research preview feature, which means:
  • The feature may change based on feedback
  • Availability and pricing are subject to change
  • The underlying API configuration may evolve
Report issues or feedback through your usual Anthropic support channels.

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See also