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Home / Reference / Slash commands

/fast

slash never mined documented JSON

A Claude Code slash command, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.

Toggle fast mode on or off. Run it while Claude is responding and Claude Code toggles fast mode without waiting for the turn to end, though the running turn finishes at its original speed. Before v2.1.242, Claude Code decided from a feature flag it fetched from Anthropic whether to run the command mid-turn or queue it until the turn finished, and always queued it in a session that doesn't fetch feature flags. Availability in non-interactive mode with -p is limited; see Toggle fast mode. Requires Claude Code v2.1.205 or later

Anthropic's own wording. Read off Commands, captured 2026-09-28.

First seen — never in a mined build
Last seen — never in a mined build
Builds0 / 150on this box, as of v2.1.309
Written about v2.1.36 first named in a changelog, 7 Feb 2026

In the changelogs

22

Releases whose published page names /fast.

  1. v2.1.299
    /effort and /fast now work in agent view

    In agent view, /effort and /fast now take effect instead of telling you to attach to a session

    found in this entry's text, named in this entry

  2. v2.1.295
    Switching fast mode can now run hooks and wait for the workspace

    Turning fast mode on or off now goes through a step that can run PreModelSwitch hooks and show "Waiting for the workspace…"

    found in this entry's text, named in this entry

  3. v2.1.288
    Permission prompts can explain why auto mode is not skipping them

    New messages explain that an action is allowed but Claude still asks, because auto mode is unavailable, and say why

    found in this entry's text

  4. v2.1.286
    /compact, /clear and /rewind ask to confirm inside an agent view

    Typing /compact, /clear or /rewind while viewing an agent now asks you to confirm running it on the main conversation

    found in this entry's text

  5. v2.1.286
    Clearer /ultrareview stop messages, plus small /fast, login and settings changes

    The /ultrareview stop and failure messages are reworded, and /fast, login status and the output style picker change slightly

    found in this entry's text, named in this entry

  6. v2.1.280
    Fast mode's default model resolution changed in prompt and code

    Fast mode's system-prompt wording and its default-model fallback in code both changed

    found in this entry's text

  7. v2.1.280
    Fast mode no longer restricted to Opus 5/4.8 in the system prompt

    The system prompt no longer says fast mode is limited to Opus 5/4.8, and now lists Opus 5.5 in the model catalog

    found in this entry's text, named in this entry

  8. v2.1.251
    Fast mode now vets the model change through a hook before applying

    Turning Fast mode on now runs your model-switch hook and can be refused.

    named in this entry, found in this entry's text

  9. v2.1.248
    Auto mode can be switched off server-side when /fast is on

    Auto mode can be disabled server-side while /fast is on, but nothing sets that today.

    named in this entry, found in this entry's text

  10. v2.1.248
    CLAUDE_CODE_ENABLE_AUTO_MODE is no longer required, or read at all

    Auto mode no longer needs CLAUDE_CODE_ENABLE_AUTO_MODE; setting it now does nothing at all.

    found in this entry's text

  11. v2.1.221
    Fast mode availability text drops Opus 4.7

    Fast mode availability text now lists only Opus 5 and 4.8.

    found in this entry's text

  12. v2.1.219
    Fast mode advertised on Opus 5 in the environment prompt

    Claude is now told Fast mode applies to Opus 5 as well as earlier models.

    found in this entry's text

  13. v2.1.196
    Fast Mode Model Scope Narrowed

    found in this entry's text

  14. v2.1.140
    Fast Mode Now Supports Opus 4.7

    found in this entry's text

  15. v2.1.122
    Fast Mode Tag in Input Box Border

    found in this entry's text

  16. v2.1.116
    /fast Command (Non-Interactive Variant)

    found in this entry's text

  17. v2.1.70
    Effort Level Indicator

    found in this entry's text

  18. v2.1.37
    Fast Mode Command Responsiveness

    found in this entry's text

  19. v2.1.36
    Fast Mode

    found in this entry's text

  20. v2.1.36
    New User Setting: fastMode

    found in this entry's text

  21. v2.1.36
    Fast Mode System Prompt Context

    found in this entry's text

  22. v2.1.36
    Interactive Fast Mode Toggle UI

    found in this entry's text

First cited

8

The earliest release whose published evidence quoted /fast was v2.1.219, 24 Jul 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.

ReleaseDateThe span that was quoted
v2.1.21924 Jul 2026It can be toggled with /fast and is available on Opus 5/4.8/4.7.
v2.1.2213 Aug 2026It can be toggled with /fast and is available on Opus 5/4.8.
v2.1.24827 Aug 2026auto mode disabled: tengu_auto_mode_config.disableFastMode with the /fast toggle on
v2.1.24827 Aug 2026auto mode unavailable while fast mode is on · run /fast off
v2.1.28022 Sep 2026Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast.
v2.1.28022 Sep 2026It can be toggled with /fast.

2 further spans in the ledger name it. The list above is the earliest first and stops at 6.

Presence across releases

0

The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.

Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the slash command does. All slash commands.

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