Subscribe to live call events (SSE)

Real-time streaming of user speech (STT) and agent speech (TTS) events for an active call via Server-Sent Events.

The connection is real-time — events stream directly from the call runtime as they are produced. The SSE connection auto-closes when the call ends (sse_close event). Only active calls can be subscribed to; completed calls return a 400 error.

Transcript event types:

• user_interim_transcription — Partial, in-progress transcription as the user speaks. Use for live preview only; will be superseded by user_transcription.
• user_transcription — Final transcription for a completed user speech turn.
• tts_completed — Fired when the agent finishes speaking a TTS segment. Includes the spoken text and optionally TTS latency.

Lifecycle events:

• sse_init — Sent immediately when the SSE connection is established.
• sse_close — Sent when the call ends, right before the server closes the connection.

Other event types (e.g. tool_call_start, pre_call_api, agent_log, metrics) are also sent on this stream.

• call_start
• call_end
• turn_latency
• metrics
• agent_node_state
• hopping
• knowledgebase
• variable_extraction
• pre_call_api
• post_call_api
• agent_error
• agent_log
• tool_call_start
• tool_call_end
• tool_call_error
• call_cancelled
• call_recording