Python SDK reference | ElevenLabs Documentation

This page documents the public API for the Speech Engine Python SDK (elevenlabs).

Getting a Speech Engine resource

Retrieve a SpeechEngineResource by its engine ID. The returned object provides methods to start a server, verify requests, or create individual sessions.

1 from elevenlabs import AsyncElevenLabs
2 
3 elevenlabs = AsyncElevenLabs()
4 engine = await elevenlabs.speech_engine.get("seng_8k3m9xr4hjnfg983brhmhkd98n6")

SpeechEngineResource

Properties

Property	Type	Description
`engine_id`	`str`	The ID of the speech engine.

serve

Start a standalone WebSocket server. Blocks until stopped.

1 await engine.serve(
2     port=3001,
3     path="/ws",
4     debug=True,
5     on_transcript=handle_transcript,
6 )

Parameter	Type	Default	Description
`port`	`int`	`3001`	Port to listen on.
`path`	`str`	`None`	Restrict connections to this path. `None` accepts all.
`debug`	`bool`	`False`	Enable debug logging to stdout.
`on_init`	`callable`		Called when a session is initialized.
`on_transcript`	`callable`		Called when a user transcript arrives.
`on_close`	`callable`		Called on clean disconnect.
`on_disconnect`	`callable`		Called when the WebSocket drops unexpectedly.
`on_error`	`callable`		Called on protocol or WebSocket errors.

verify_request

Verify that an incoming request originates from the ElevenLabs Speech Engine API. Checks the X-Elevenlabs-Speech-Engine-Authorization header for a valid JWT signed with the SHA-256 hash of your API key.

Only needed when managing the WebSocket upgrade yourself. When using serve(), verification is handled automatically.

1 is_valid = engine.verify_request(headers)

Parameter	Type	Description
`headers`	`dict`	Request headers dictionary.

Returns: bool — True if the request is valid.

create_session

Wrap an accepted WebSocket in a SpeechEngineSession. Use this for custom server integration (e.g. FastAPI, Starlette, or manual WebSocket handling).

1 session = engine.create_session(websocket, debug=True)
2 session.on("user_transcript", handle_transcript)
3 await session.run()

Parameter	Type	Default	Description
`ws`	WebSocket		An accepted WebSocket connection.
`debug`	`bool`	`False`	Enable debug logging.

Returns: SpeechEngineSession

SpeechEngineSession

Wraps a single WebSocket connection. Each connection represents one conversation. The session emits events for transcripts and lifecycle changes, and provides methods to send LLM responses back.

When a new transcript arrives, the previous transcript handler is cancelled automatically, interrupting any in-flight LLM call.

Properties

Property	Type	Description
`conversation_id`	`Optional[str]`	The conversation ID assigned by the API. Available after `init`.
`is_open`	`bool`	Whether the session is still open.

on

1 session.on("user_transcript", handler)

off

Remove a previously registered handler.

1 session.off("user_transcript", handler)

once

1 session.once("init", handler)

send_response

Send an LLM response back to the Speech Engine API for text-to-speech synthesis. Must be called inside an on_transcript handler. Calling it outside of a handler emits a warning and returns without sending.

1 # String response
2 await session.send_response("Hello, how can I help?")
3 
4 # Streamed response (OpenAI, Anthropic, or Gemini)
5 stream = await openai_client.responses.create(model="gpt-4o", input=messages, stream=True)
6 await session.send_response(stream)

Parameter	Type	Description
`response`	`str` \| async iterable	A complete string or an async iterable of text chunks / LLM stream events.

The SDK auto-detects and extracts text from the following LLM stream formats:

Provider	Event format
OpenAI Responses API	`{ type: "response.output_text.delta", delta: "text" }`
OpenAI Chat Completions	`{ choices: [{ delta: { content: "text" } }] }`
Anthropic Messages API	`{ type: "content_block_delta", delta: { type: "text_delta", text: "text" } }`
Google Gemini API	`{ candidates: [{ content: { parts: [{ text: "text" }] } }] }`

run

Run the receive loop until the WebSocket closes. This is the main entry point after constructing a session manually via create_session().

1 session = engine.create_session(websocket)
2 session.on("user_transcript", handle_transcript)
3 await session.run()

close

Close the session and the underlying WebSocket connection.

1 session.close()

Callbacks

The keyword arguments passed to serve(). All callbacks are optional. Handlers can be synchronous or asynchronous (coroutine) functions.

Callback	Signature	Description
`on_init`	`(conversation_id: str, session) -> None`	Session initialized with a conversation ID.
`on_transcript`	`(transcript: list, session) -> None`	User speech transcribed.
`on_close`	`(session) -> None`	Clean disconnect from ElevenLabs.
`on_disconnect`	`(session) -> None`	WebSocket dropped unexpectedly.
`on_error`	`(error: Exception, session) -> None`	Protocol or WebSocket error.

Events

When using session.on() directly instead of callbacks, these are the event names and their handler signatures.

Event	Handler signature
`user_transcript`	`(transcript: list[ConversationMessage])`
`init`	`(conversation_id: str)`
`close`	`()`
`disconnected`	`()`
`error`	`(error: Exception)`

Event name constants are available for type-safe usage:

1 from elevenlabs.speech_engine import USER_TRANSCRIPT, INIT, CLOSE, DISCONNECTED, ERROR
2 
3 session.on(USER_TRANSCRIPT, handle_transcript)

ConversationMessage

A single message in the conversation history. The full transcript is passed to on_transcript on every turn.

Property	Type	Description
`role`	`"user"` \| `"agent"`	Who sent the message.
`content`	`str`	The text content of the message.

Wire protocol

For reference, these are the JSON messages exchanged over the WebSocket connection. The SDK handles serialization and deserialization automatically.

Incoming (ElevenLabs API to developer server)

Message type	Fields	Description
`init`	`conversation_id: string`	Session initialized.
`user_transcript`	`user_transcript: TranscriptMessage[]`, `event_id: number`	User speech transcribed.
`ping`		Keep-alive. SDK responds with pong.
`close`		Clean disconnect.
`error`	`message: string`	Error from the API.

Outgoing (developer server to ElevenLabs API)

Message type	Fields	Description
`agent_response`	`content: string`, `event_id: number`, `is_final: boolean`	LLM response chunk for TTS synthesis.
`pong`		Response to ping.