AsyncAPI channel · Retell AI
· Retell AI Custom LLM WebSocket
/llm-websocket/{call_id}
The single bidirectional channel for one call. Retell sends
ping_pong / call_details / update_only / response_required /
reminder_required events to your server; your server replies with
config / ping_pong / response / agent_interrupt / tool_call_invocation /
tool_call_result / update_agent / metadata events.
Provider:Retell AIAsyncAPI: v2.6.0Spec: Retell AI Custom LLM WebSocketOperations: 2Messages: 12
Channel address
/llm-websocket/{call_id}
Parameters
call_id — Unique id of the call.
Operations
publish
sendToRetell
Messages your server sends to Retell.
subscribe
receiveFromRetell
Messages Retell sends to your server.
Messages
config
Optional initial config your server sends to Retell.
Content-Type: application/json
ping_pong
Keep-alive acknowledgment.
Content-Type: application/json
response
Streams the agent's spoken content for a response_id.
Content-Type: application/json
agent_interrupt
Injects an immediate agent utterance out of the normal response cycle.
Content-Type: application/json
tool_call_invocation
Records that the agent invoked a tool (for the transcript/logs).
Content-Type: application/json
tool_call_result
Records the result returned from a previously invoked tool.
Content-Type: application/json
update_agent
Applies runtime agent-config changes mid-call.
Content-Type: application/json
metadata
Arbitrary JSON forwarded to the frontend / web client.
Content-Type: application/json
call_details
Initial call metadata, sent once at connection if enabled in config.
Content-Type: application/json
update_only
Transcript and turn-taking update that does not require a response.
Content-Type: application/json
response_required
Retell requests an agent response for the given response_id.
Content-Type: application/json
reminder_required
Retell requests a reminder utterance after user silence.
Content-Type: application/json
About AsyncAPI
The AsyncAPI specification describes event-driven APIs the way OpenAPI describes request/response APIs. A channel is the named pipe — a webhook URL, a Kafka topic, a WebSocket route, an MQTT subject — that producers and consumers publish or subscribe to. Each channel carries one or more messages with structured payloads, and an operation declares whether a given party sends or receives on that channel.