Fast Mode Command Responsiveness / Claude Code v2.1.37

The /fast command now includes a 300ms timeout for the status prefetch, ensuring the command remains responsive even when the API is slow.

Evidence

Timeout with telemetry tracking (search for "tengu_fast_mode_prefetch_timeout")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

How sure we are

One source agreesOne thing we can check says the same as this entry.

Anthropic's release notes agreeFixed an issue where /fast was not immediately available after enabling /extra-usage

See this entry in the whole of v2.1.37 →

The build it came inv2.1.37

7 Feb 2026 · 2 entries, this one is #2.

Either side of it

v2.1.36Older
v2.1.38Newer

Open the release →

Names in this entry

slash/fast
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
flagtengu_fast_mode_prefetch_timeout

Anthropic's note

Upstream's own release notes for v2.1.37 name something this entry names, so the two are probably about the same change. Probably: the pairing is made on a shared name rather than on the words around it.

Fixed an issue where /fast was not immediately available after enabling /extra-usage

Is this right?