agent.spawn
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.
A plugin hook can block a subagent from starting or change which model it uses.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.242.
In the changelogs
16Releases whose published page names agent.spawn.
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v2.1.299
Plugin hook denials now carry a reason
Default deny responses for plugin hooks such as tool.check and agent.spawn now include a reason alongside the decision
found in this entry's text
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v2.1.299
Subagents refused a different working folder now fail with a clear error
If a subagent is not allowed to run in another folder, Claude Code now stops before starting it and says to start it without cwd
found in this entry's text
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v2.1.289
Teammate spawning keeps more detail about how each teammate was started
Teammate records gain a field for how they were spawned, and the agent.spawn hook gains an entry for an argument that was not applied
found in this entry's text
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v2.1.289
Plugin agent-launch hooks now also apply to teammates
Starting a named teammate now goes through a plugin's agent-launch hook, which can block, rewrite or retype it
named in this entry, found in this entry's text
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v2.1.280
MCP-required-missing agent spawn errors now carry structured data
Errors for missing required MCP servers during agent spawning now include structured error data, not just a text message
found in this entry's text
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v2.1.269
$.agent.spawn SDK call now returns an agentId on success
The agent.spawn plugin action now returns the new agent's ID on success
found in this entry's text
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v2.1.269
agent.spawn hook logging drops the resolved-model detail
Debug logs for a hook rewriting a subagent's model no longer show what the model resolves to, just the raw before/after values
found in this entry's text
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v2.1.269
"agent.spawn" hook dispatch reworked behind an XS() check whose default I could not pin down
New agent-spawn entry point only runs agent.spawn hooks when an internal check passes
found in this entry's text, named in this entry
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v2.1.267
Policy checks for agent.spawn and tool.call gain argument restoration
Policy checks for spawning agents and calling tools now restore pinned fields a hook altered, not just flag them
found in this entry's text
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v2.1.260
New spawn-hook error: worktree/cwd conflict
Spawn hooks setting both cwd and worktree isolation now fail with a clear error.
found in this entry's text
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v2.1.260
New spawn-hook error: permission-rule conflicts with rewritten spawn
Spawn hooks that conflict with a permission rule now block the launch with an explicit error.
found in this entry's text
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v2.1.260
Web-fetch agent retype via spawn hook is blocked without classifier review
Spawn hooks can no longer redirect a web-fetch to an unconfined agent without classifier review.
found in this entry's text
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v2.1.260
Plugin agent.spawn hooks can now rewrite or deny subagent launches
Plugin hooks can now deny or rewrite subagent launches before they start.
found in this entry's text, named in this entry
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v2.1.242
A plugin hook can block a subagent from launching
A plugin hook can block a subagent from starting or change which model it uses.
found in this entry's text
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v2.1.242
Each hook event enforces what a plugin is allowed to change
Plugin hooks are limited in what they may rewrite, and cannot take over question prompts.
found in this entry's text
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v2.1.242
Plugin modules with a
$API that can hook events and redraw the terminal UIPlugins can install code that intercepts tool calls and repaints parts of the terminal interface.
found in this entry's text
First cited
6The earliest release whose published evidence quoted agent.spawn was v2.1.260, 3 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.