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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.299 ·

Agent tool changes when subagents run in the background

Agent tool calls can now default to running in the background, a new message can refuse background launches, and the tool checks working folders

Group of 2 You'll notice Improvements
JSON All of v2.1.299
You'll noticeTier: how much it should matter to you
3Useful: my rating, 1 to 5
4Signal: worth watching, 1 to 5
SubagentsArea: what it touches
ImprovementsKind: in v2.1.299,
What probably matters to youSection of the release

Unclear It is not clear what decides whether a subagent now defaults to the background.

What

The Agent tool lets Claude start a subagent, a helper that works on a task on its own. Its run_in_background setting decides whether the subagent runs in the background while Claude keeps going.

  • Before, a subagent ran in the background only when run_in_background was exactly true. A new default helper now also takes part, so run_in_background can default to background.
  • launchedWithDefaults is sent only when a helper is on.
  • A new fixed message tells Claude that background agents cannot be started in this session right now, and to run the agent with run_in_background: false. Where this message is returned was not found.
  • The tool checks the cwd (the working folder) on each call, and again after a spawn hook rewrites the call. A hook is a user-set command that runs at certain moments.
  • The tool takes a timing object and marks time spent waiting on outside work.

The stock Agent tool description captured under this release is unchanged.

Why

Subagents may start running in the background in cases where they did not before, and some background launches may be refused with the new message.

Read from
Names in the bundlerun_in_background
Since it was published

The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.

Confirmed since Anthropic's documentation has since written up run_in_background, on Use the mods API. | [`$.tool.call`](/docs/en/plugins/mods/reference#mods-api-methods) of Bash with `run_in_background: true`, Monitor, or CronCreate | Resolves with `{ deny: '<tool> was not run: it starts background work, a schedule or a goal, and <reason>'… plugins/mods/api see the edit
Added since A small documentation edit on Orchestrate teams of Claude Code sessions touched a line naming run_in_background after this was published. * **No background subagents from in-process teammates**: an in-process teammate's own subagents run in the foreground, because a teammate's background work can't outlive the lead's process. Claude Code returns an error when a teammate spaw… agent-teams see the edit
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtIt is not clear what decides whether a subagent now defaults to the background.
Anthropic's documentation agreesA small documentation edit on Orchestrate teams of Claude Code sessions touched a line naming run_in_background after this was published.

See this entry in the whole of v2.1.299 →

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