handbackOptIn
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.
Async sub-agents can now explicitly hand control back to the agent that owns them
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.267.
In the changelogs
2Releases whose published page names handbackOptIn.
-
v2.1.267
Async sub-agents gain a 'handback' mechanism for returning control to the parent
Async sub-agents can now explicitly hand control back to the agent that owns them
found in this entry's text, named in this entry
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v2.1.267
Agent tool completion gains a 'handback' delivery mechanism
Agent tool completion adds a 'handback' mechanism to deliver results to the calling agent
found in this entry's text
First cited
2The earliest release whose published evidence quoted handbackOptIn was v2.1.267, 9 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.