session.attach
A Claude Code settings key, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
Plugin hooks can now react to tool-call dry-runs, config changes, and session attach/detach events.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.269.
In the changelogs
4Releases whose published page names session.attach.
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v2.1.275
New plugin/session lifecycle hook events session.end and session.measure
Two new lifecycle events,
session.endandsession.measure, added for plugins and hooksfound in this entry's text
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v2.1.269
Plugin hooks engine gains new event types: tool.check, config.set, config.describe, session.attach, session.detach, plugin.register
Plugin hooks can now react to tool-call dry-runs, config changes, and session attach/detach events.
found in this entry's text, named in this entry
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v2.1.269
New internal plugin/hook lifecycle events added
Five new internal plugin/hook lifecycle events were added: tool.check, config.set, config.describe, session.attach, session.detach
found in this entry's text, named in this entry
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v2.1.269
New plugin hook events: session.attach, session.detach, tool.check
Plugins can now hook into session attach/detach and tool permission checks
found in this entry's text, named in this entry
First cited
3The earliest release whose published evidence quoted session.attach was v2.1.269, 11 Sep 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 below.
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.
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 settings key does. All settings keys.