Delegation depth

Every task token names its agent in act, with depth: 1.

Sub-agent delegation is not in v0.1

The control plane issues depth: 1 only. An exchange validates its subject token against your identity provider, so a task token presented as a subject token is invalid_grant. An agent cannot exchange its task token for a token for another agent. Do not build anything that expects Subact ID to issue a deeper chain.

The claim shape

RFC 8693 lets act nest, and the specification defines how a chain would look, with the human still in sub. Subact ID does not issue this in v0.1:

{
  "sub": "f47ac10b-58cc-4372-a567-0e02b2c3d479",
  "act": {
    "sub": "agent:db-reader",
    "depth": 2,
    "act": { "sub": "agent:jira-triage", "depth": 1 }
  }
}

The outermost act would be the agent that made the call. The server SDKs still read and limit this shape, as section 9 of the spec requires of every tool server.

Where depth is limited

On the registration. max_delegation_depth is required on every agent registration and accepts 1 to 5. The control plane checks it on every exchange, against a depth that is always 1 in v0.1, so the value does not change what is issued. Set it to 1.

On the tool server. @subactid/server and @subactid/mcp refuse a token whose act chain is deeper than maxDelegationDepth, which defaults to 1. A deeper token is refused with 403 delegation_too_deep. With tokens from Subact ID v0.1, the default of 1 accepts everything the control plane issues, so leave it unset.