Streaming events

Wire format

There are no event: lines. Every frame arrives as a default SSE message, and the event name is the type field inside the JSON payload.

First frame

data: {"type":"response.created","sequence_number":0,"response":{"id":"resp_...","status":"in_progress","metadata":{"session_id":"hsess..."}}}

Important events

• response.created: Save response.id and response.metadata.session_id immediately.
• response.output_text.delta: Append visible answer text.
• response.output_item.added: Show sanitized tool or activity progress.
• response.completed: Finalize successful UI state.
• response.incomplete: Show partial result and offer Continue when appropriate.
• response.failed: Show the classified failure or cancellation state.

Open standard
Data-only SSE frames carrying type and sequence_number, ending in exactly one terminal event, are the wire rules that UHP's Streaming chapter makes normative for every conformant server. See the Streaming chapter of the Unified Harness Protocol.