agent.register
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 SDK adds agent.register and session.refreshAgents, plus a one-shot flag for whether the system prompt was delivered
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.274.
In the changelogs
4Releases whose published page names agent.register.
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v2.1.290
Plugins now get a notice when their text is cut short
Over-long plugin text is now shortened with an ellipsis and a notice, and long tool descriptions are cut instead of rejected
found in this entry's text
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v2.1.277
Plugin hook dispatch deep-copies input for a fixed set of UI/registration events
Plugin hooks now receive a deep copy of the event payload for UI and registration events, not the original
found in this entry's text
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v2.1.274
Plugin SDK ($.) gains agent.register and session.refreshAgents, plus a system-prompt-delivered flag consumable once
Plugin SDK adds agent.register and session.refreshAgents, plus a one-shot flag for whether the system prompt was delivered
named in this entry, found in this entry's text
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v2.1.274
SDK gains an agent.register call
SDK adds an agent.register call for defining named agents programmatically
named in this entry, found in this entry's text
First cited
1The earliest release whose published evidence quoted agent.register was v2.1.274, 16 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.