What it is
After the session's model changes, including changes Claude Code makes on its own, such as restoring the model when you resume a session
Anthropic's own wording. Read off Hooks reference, captured 2026-09-22.
Presence across releases
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.
First cited
1The earliest release whose published evidence quoted PostModelSwitch was v2.1.251, 28 Aug 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table above.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the hook event does. All hook events.