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livekit-plugins-slng adds STT and TTS adapters for LiveKit Agents. It lets you use any model on the SLNG gateway from within a LiveKit agent.

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Prerequisites

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Installation

pip install livekit-plugins-slng

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Credentials

You need an SLNG API key. The plugin reads it from the SLNG_API_KEY environment variable automatically: 
export SLNG_API_KEY="your-slng-api-key"
You can also pass it explicitly via api_key: 
stt = slng.STT(api_key="your-slng-api-key", model="deepgram/nova:3")

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Quickstart

Create an STT and TTS instance, then pass them to your LiveKit agent session: 
from livekit.plugins import slng

stt = slng.STT(
    api_key="your-slng-api-key",
    model="deepgram/nova:3",
    language="en",
)

tts = slng.TTS(
    api_key="your-slng-api-key",
    model="deepgram/aura:2",
    voice="aura-2-thalia-en",
    language="en",
)

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Full voice agent example

This example wires up STT, TTS, and VAD into a complete LiveKit agent that greets the user on join: 
from livekit.agents import Agent, AgentSession, JobContext, WorkerOptions, cli
from livekit.plugins import silero, slng

SLNG_API_KEY = "your-slng-api-key"


class MyAgent(Agent):
    async def on_enter(self):
        await self.session.say("Hello! How can I help?")


async def entrypoint(ctx: JobContext):
    await ctx.connect()

    stt = slng.STT(
        api_key=SLNG_API_KEY,
        model="deepgram/nova:3",
        language="en",
        sample_rate=16000,
        enable_partial_transcripts=True,
    )

    tts = slng.TTS(
        api_key=SLNG_API_KEY,
        model="deepgram/aura:2",
        voice="aura-2-thalia-en",
        language="en",
        sample_rate=24000,
    )

    session = AgentSession(
        stt=stt,
        tts=tts,
        vad=silero.VAD.load(),
        turn_detection="vad",
        allow_interruptions=True,
    )

    await session.start(agent=MyAgent(), room=ctx.room)


if __name__ == "__main__":
    cli.run_app(WorkerOptions(entrypoint_fnc=entrypoint))

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Model identifiers

Models follow the format provider/model:variant. Prefix with slng/ to target an SLNG-hosted instance: 
provider/model:variant          # third-party passthrough
slng/provider/model:variant     # SLNG-hosted
Examples: 
model="deepgram/nova:3"              # Deepgram Nova 3 (passthrough)
model="slng/deepgram/nova:3-en"      # SLNG-hosted Deepgram Nova 3, English
model="elevenlabs/eleven-flash:2.5"  # ElevenLabs Flash v2.5 (passthrough)
See the Models page for the full list of available models.

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STT reference

slng.STT streams speech-to-text over WebSocket. It supports multi-endpoint failover.

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Constructor

stt = slng.STT(
    api_key="your-slng-api-key",          # Required. SLNG API key.
    model="deepgram/nova:3",              # Model identifier. Default: "deepgram/nova:3"
    language="en",                         # Language code. Default: "en"
    sample_rate=16000,                     # Audio sample rate in Hz. Default: 16000
    encoding="pcm_s16le",                  # Audio encoding: "pcm_s16le" or "pcm_mulaw". Default: "pcm_s16le"
    buffer_size_seconds=0.064,             # Audio buffer size in seconds. Default: 0.064
    enable_partial_transcripts=True,       # Enable interim results. Default: True
    enable_diarization=False,              # Enable speaker identification. Default: False
    min_speakers=None,                     # Minimum speakers for diarization. Default: None
    max_speakers=None,                     # Maximum speakers for diarization. Default: None
    vad_threshold=0.5,                     # Voice activity detection threshold. Default: 0.5
    vad_min_silence_duration_ms=300,       # Minimum silence for VAD (ms). Default: 300
    vad_speech_pad_ms=30,                  # Speech padding for VAD (ms). Default: 30
    model_endpoint=None,                   # Optional explicit WebSocket endpoint URL
    model_endpoints=None,                  # Optional list of failover endpoints
)

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Endpoint failover

Pass a list of endpoints to model_endpoints. If the first one fails, the plugin tries the next in order: 
stt = slng.STT(
    api_key=SLNG_API_KEY,
    model_endpoints=[
        "wss://api.slng.ai/v1/stt/deepgram/nova:3",
        "wss://api.slng.ai/v1/stt/slng/deepgram/nova:3-en",
    ],
    language="en",
)

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Default endpoint

If model_endpoint is omitted, the plugin connects to: 
wss://api.slng.ai/v1/stt/{model}

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TTS reference

slng.TTS streams text-to-speech over WebSocket with connection pooling.

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Constructor

tts = slng.TTS(
    api_key="your-slng-api-key",          # Required. SLNG API key.
    model="deepgram/aura:2",              # Required. Model identifier.
    voice="aura-2-thalia-en",             # Voice identifier. Default: "default"
    language="en",                         # Language code. Default: "en"
    sample_rate=24000,                     # Audio sample rate in Hz. Default: 24000
    speed=1.0,                             # Speech speed multiplier. Default: 1.0
    model_endpoint=None,                   # Optional explicit WebSocket endpoint URL
)

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Streaming vs batch

  • tts.stream() sends text word-by-word and returns audio chunks in real time. Use this for voice agents.
  • tts.synthesize(text) does one-shot synthesis. Works fine for previews, but stream() is better for interactive agents.

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Default endpoint

If model_endpoint is omitted, the plugin connects to: 
wss://api.slng.ai/v1/tts/{model}

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Voice selection

Pick a voice that matches your chosen model. See the Voices pages for what’s available per provider.
The plugin outputs linear16 PCM audio internally and registers itself with LiveKit on import. Both STT and TTS authenticate with api_key.
When new models are added to the SLNG gateway, you can use them right away without updating the plugin.

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Next steps

  • Browse available Models for STT and TTS
  • Check the Voices pages for voice options per provider
  • See Voice Agents for the SLNG-managed agents API