The summary field on task status objects is now documented to clarify its source: for a local_agent task it is a model-generated progress summary, shown only when agentProgressSummaries is enabled, while for a backgrounded mcp_task it is the MCP server's own status message and is always emitted.
Names in the bundleagentProgressSummaries
Documented inclaude-code/agent-sdk/typescript
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 agentProgressSummaries, on Agent SDK reference - TypeScript.
For a subagent task, the `summary` field carries a model-generated progress summary and is populated only when [`agentProgressSummaries`](#options) is enabled. For a [backgrounded MCP tool call](/docs/en/mcp#automatic-backgrounding-of-long…agent-sdk/typescript 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 agentProgressSummaries, on Agent SDK reference - TypeScript.