# 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](https://unifiedharnessprotocol.org/spec/streaming).