Sweep 19 Sep 2026 · 02:36Z Build v2.1.278 500 read Stable v2.1.267 Latest v2.1.278 Next v2.1.278 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.277 ·

Long-running tool calls can now detach to the background instead of blocking new messages

A slow tool call can now move to the background so a new message gets through, with its result delivered later

TierYou'll noticehow much it should matter to you
Useful5my rating, 1 to 5
Signal4worth watching, 1 to 5
AreaBackground Taskswhat it touches
KindNew Featuresin v2.1.277,
Group of 2 You'll notice Notable

A slow tool call can now move to the background so a new message gets through, with its result delivered later

What

If a tool call is still running when the user sends a new message, Claude Code can now move that call to the background ('detach' it) instead of making the new message wait for the tool to finish.

  • The model is told via an injected note that the call 'was not interrupted' and that its result 'will be delivered to you on its own, in a later tool_result carrying this tool_use_id'.
  • When the detached call eventually finishes, completes, fails, times out, or is stopped, its result is delivered as a task notification.
  • Detachment is capped: a detached call is force-aborted after 5 minutes if it hasn't finished.
  • The event tengu_tool_call_detached is emitted for telemetry.

Why

This stops a single slow tool call from blocking the whole conversation. A new message can get through immediately while the original tool keeps running in the background, with its result delivered whenever it's ready.

Read from
Feature flag
tengu_tool_detach Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.277: on

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.277. It isn't a statement about your account. What a flag value here can and cannot tell you

How sure we are
One source agreesOne thing we can check says the same as this entry.
The name it cites is new in this buildNew in this build: tengu_tool_detach

See this entry in the whole of v2.1.277 →