item_id: str

The unique identifier of the MCP tool call item being processed.

output_index: int

The index of the output item in the response’s output array.

sequence_number: int

The sequence number of this event.

type: Literal["response.mcp_call.in_progress"]

The type of the event. Always ‘response.mcp_call.in_progress’.

agent: Optional[Agent]

The agent that owns this multi-agent streaming event.

agent_name: str

The canonical name of the agent that produced this item.