What
A subagent is a helper agent that Claude starts to work on part of a task. Claude can resume a subagent that was paused. Before, a resumed subagent that Claude waited on in place always held up Claude's turn until it finished. Waiting on one can now end by moving it to the background, so Claude's turn carries on. This happens:
- when the subagent is already running in the background
- when it has its own child tasks still being kept alive
- after about two minutes (120000 milliseconds), when
CLAUDE_AUTO_BACKGROUND_TASKSis set
Resuming also has a new "call" mode. A resumed subagent can pick up a tool call it was waiting on, where a tool call is one action such as running a command or reading a file.
Why
A resumed subagent can no longer block Claude's turn for a long stretch. If you set CLAUDE_AUTO_BACKGROUND_TASKS, the two-minute limit now applies to resumed subagents as well.