What
The assistant-message schema now states that one message is emitted per completed content block, that consecutive messages can share the same message.id, that stop_reason is null and usage is not final on those, and that parent_tool_use_id is set inside a subagent.
Evidence
the turn's stop reason and total usage arrive on the result message
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
Names in the bundleparent_tool_use_idstop_reason
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up stop_reason, on List Events.
The id of the `agent.tool_use` or `agent.mcp_tool_use` event this result corresponds to, which can be found in the last `session.status_idle` [event's](https://platform.claude.com/docs/en/api/beta/sessions/events/list#beta_managed_agents_s…api/beta/sessions/events/list see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up stop_reason, on List Events.