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When using the real-time WebSocket APIs (tts_realtime or stt_realtime), two parameters control how the connection initialises. Both work identically across TTS and STT. For the full protocol lifecycle, including raw WebSocket messages, browser tokens, multiplexing, and error behavior, see WebSocket Lifecycle.

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send_setup_on_start

Controls whether the setup message is automatically sent when the context manager is entered. Defaults to True. Set this to False when you need to send setup manually, for example when using multiplexing where each request has its own setup with a unique client_req_id. 
# Setup sent automatically (default)
async with client.tts_realtime(voice_id="YTpq7expH9539ERJ", output_format="pcm") as stream:
    await stream.send_text("Hello")

# Setup sent manually
async with client.tts_realtime(send_setup_on_start=False) as stream:
    await stream.send_setup({"voice_id": "YTpq7expH9539ERJ", "output_format": "pcm"})
    await stream.send_text("Hello")

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wait_for_ready_on_start

Controls whether the client blocks waiting for the server’s ready message after sending setup. Defaults to False. When set to False, the ready message is captured lazily during the normal receive loop. This reduces connection latency since you can start sending data immediately after setup without waiting for a round-trip. When set to True, stream.ready is guaranteed to be populated before you start sending data, which can be useful if you need server-provided metadata (like sample rate) before proceeding. 
# Non-blocking (default), ready captured lazily during recv
async with client.tts_realtime(
    voice_id="YTpq7expH9539ERJ",
    output_format="pcm"
) as stream:
    # stream.ready is None here, start sending immediately
    await stream.send_text("Hello")
    await stream.send_eos()

    async for msg in stream:
        # stream.ready gets populated when the ready message arrives
        if msg["type"] == "audio":
            process_audio(msg["audio"])

# Blocking, wait for ready before sending
async with client.tts_realtime(
    voice_id="YTpq7expH9539ERJ",
    output_format="pcm",
    wait_for_ready_on_start=True
) as stream:
    # stream.ready is populated here
    print(f"Server ready: {stream.ready}")
    await stream.send_text("Hello")
Both parameters work identically for stt_realtime: 
async with client.stt_realtime(
    model_name="default",
    input_format="pcm",
    wait_for_ready_on_start=True
) as stream:
    print(f"Server ready: {stream.ready}")
    await stream.send_audio(audio_data)