Sub-Agents Now Run in the Background by Default
Claude Code sub-agents now run in the background by default — Claude keeps working on the main thread while a spawned sub-agent executes, rather than blocking until it returns. This is a default-behaviour change rather than a new capability: the underlying background execution model already existed (it's the same mechanism /code-review adopted on June 20), but sub-agents generally now inherit it without needing an explicit flag.
If you've built prompts or scripts around sub-agents that assumed blocking behaviour — waiting for a sub-agent's result before the next step — check whether that assumption still holds after this default flip. Most workflows benefit from the change, but anything relying on strict ordering may need an explicit "wait for" instruction that wasn't previously necessary.