What
The SessionStart hook pipeline, which runs when a session begins or resumes, now accepts an abort signal. If that signal fires before the hooks finish, Claude Code returns whatever hook messages were already collected instead of continuing on to steps like reloading skills or checking watched paths.
Why
This allows session startup to be cut short cleanly if needed, without waiting for every SessionStart hook step to finish first.
Names in the bundleSessionStart
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.
Added since
A small documentation edit on Hooks reference touched a line naming SessionStart after this was published.
The same wait applies at launch, including a resumed session: a prompt you send while SessionStart hooks are still running doesn't reach Claude until they finish.hooks see the edit
Confirmed since
Anthropic's documentation has since written up SessionStart, on Claude Code changelog.
* Improved hook feedback: while a SessionStart, UserPromptSubmit, PreToolUse or SessionEnd hook runs, the spinner says so with elapsed time, and Esc cancels a prompt waiting on a SessionStart hookchangelog see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up SessionStart, on Claude Code changelog.