SessionStart hooks now receive an extra agentContext parameter when they run
A hook is a script you configure to run automatically at certain points in a session. The internal function that runs SessionStart hooks (which fire when a session begins or resumes) and loads plugin hooks now also accepts and passes along a new agentContext parameter, alongside existing options like credentials, the cancellation signal, and whether the session is orphaned.
This gives the hook-running machinery more context about the agent it's running for, though the finding doesn't specify what new behavior this enables for hook authors.
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.
* **One repository per session**: a session with several repositories doesn't load hooks from any repository's `.claude/settings.json`, so a SessionStart hook you define there doesn't run. Install dependencies for those sessions with a [se…cloud-environments see the edit
What information agentContext carries or what new capability it gives to SessionStart hooks is not stated.
Anthropic's documentation has since written up SessionStart, on Configure cloud environments.