pipecat-slng 0.4.0

SLNG STT/TTS services for Pipecat (WebSocket + HTTP)

pipecat-slng

Built and maintained by the SLNG team (slng.ai).

WebSocket STT and TTS services for Pipecat, backed by SLNG — a unified voice AI gateway that routes to multiple STT/TTS providers (Deepgram, ElevenLabs, Rime, Sarvam, and more) through a single API key. Swap the model string to switch providers; no other code changes needed.

Tested with Pipecat v1.3.0.

Installation

uv add pipecat-slng
# or
pip install pipecat-slng

Environment variables

SLNG_API_KEY=your_slng_api_key      # get one at https://slng.ai
OPENAI_API_KEY=your_openai_api_key  # only needed for the example bot (LLM)

Copy .env.example to .env to get started.

Usage (streaming WebSocket — recommended)

SlngSTTService and SlngTTSService run over WebSocket: low-latency, supports mid-utterance interruption, and exposes the full SLNG config surface (encoding, sample_rate, language, speed).

import os

from pipecat_slng import SlngSTTService, SlngTTSService

stt = SlngSTTService(
    api_key=os.getenv("SLNG_API_KEY"),
    model="slng/deepgram/nova:3-en",
)

tts = SlngTTSService(
    api_key=os.getenv("SLNG_API_KEY"),
    model="slng/deepgram/aura:2-en",
    voice="aura-2-thalia-en",
)

Common runtime knobs are top-level kwargs (e.g. language=, speed=, enable_vad=, enable_partials=). For richer overrides pass a SlngSTTSettings(...) / SlngTTSSettings(...) to settings=.

Defaults when not specified: STT uses language=Language.EN, enable_vad=True, enable_partials=True; TTS uses language=Language.EN and the server's default speed.

Two behaviors worth knowing:

• Confidence filter (STT). When the provider surfaces a confidence score, transcripts below 0.5 are dropped.
• Runtime settings updates. Changing voice, speed, or language mid-session (via Pipecat settings updates) reconnects the WebSocket to re-run the init handshake — expect a brief reconnect, not a silent no-op.

HTTP TTS (non-streaming fallback)

For simple request/response synthesis where streaming is not required, use SlngHttpTTSService. It issues one HTTP POST per utterance and returns the full audio body in one frame.

import os

from pipecat_slng import SlngHttpTTSService

tts = SlngHttpTTSService(
    api_key=os.getenv("SLNG_API_KEY"),
    model="slng/deepgram/aura:2-en",
    voice="aura-2-thalia-en",
)

HTTP contract limits. Per the SLNG Unified TTS HTTP OpenAPI, the request body accepts only {text, voice} — there is no config object. Encoding, sample_rate, language, and speed are therefore not configurable over HTTP; the server returns its default audio format. The service auto-detects WAV (decoded to raw PCM at the file's sample rate) and plain PCM (passed through at the pipeline's sample rate). Compressed responses (MP3/Ogg) yield an ErrorFrame — use the streaming SlngTTSService if you need codec control.

An aiohttp.ClientSession is created internally if you don't pass one; supply aiohttp_session=... to reuse a shared session.

Region routing

Both services support gateway region routing via region_override (pin to a datacenter: ap-southeast-2 | eu-north-1 | us-east-1) and world_part_override (broad zone: ap | eu | na). When both are set, region_override wins. WebSocket services send these as the X-Region-Override / X-World-Part-Override headers; the HTTP service uses the region / world-part query parameters (per the bridge contract).

stt = SlngSTTService(
    api_key=os.getenv("SLNG_API_KEY"),
    model="slng/deepgram/nova:3-en",
    region_override="eu-north-1",
)

Model routing & bring-your-own-key (BYOK)

The model string decides where transcription/synthesis runs:

• slng/... (e.g. slng/deepgram/aura:2-en) — hosted by SLNG.
• anything else (e.g. deepgram/aura:2, elevenlabs/..., cartesia/sonic:3, sarvam/bulbul:v3) — an external provider, proxied through SLNG.

An external route works with or without your own provider key — those are two independent choices. The slng/ prefix is what selects SLNG-hosted; BYOK is a separate decision layered on top. The full matrix:

model	provider_key	Runs on	Billed by
slng/deepgram/aura:2-en	—	SLNG (self-hosted)	SLNG (audio-minutes)
deepgram/aura:2	—	SLNG's own provider account	SLNG (audio-minutes)
deepgram/aura:2	your key	your provider account	the provider (BYOK)
slng/...	your key	—	rejected — HTTP 400

For BYOK, pass your own provider key via provider_key. It is forwarded as the X-Slng-Provider-Key header, so the provider bills your account directly and no SLNG audio-minute fees apply — the SLNG cache still applies on top. This is a separate key from SLNG_API_KEY, which always authenticates you to SLNG. See the BYOK docs.

# BYOK = an external route + your own provider key. Deepgram is shown here; the
# same pattern works for any external provider (ElevenLabs, Cartesia, Sarvam, …).
stt = SlngSTTService(
    api_key=os.getenv("SLNG_API_KEY"),            # authenticates you to SLNG
    model="deepgram/nova:3",                      # external route — no slng/ prefix
    provider_key=os.getenv("SLNG_PROVIDER_KEY"),  # your own provider key
)

tts = SlngTTSService(
    api_key=os.getenv("SLNG_API_KEY"),
    model="deepgram/aura:2",                      # external route — no slng/ prefix
    voice="aura-2-thalia-en",
    provider_key=os.getenv("SLNG_PROVIDER_KEY"),
)

BYOK is valid only on external routes; an slng/... route plus a provider_key is rejected with a 400 ("BYOK is only supported for external STT/TTS routes"). If the provider rejects your key, the failure surfaces as a backend_connection_failed error frame over WebSocket, or the upstream 401/403 with the X-Slng-Auth-Source: client_key response header over HTTP.

Example

A complete cascade bot (STT → LLM → TTS, WebSocket TTS by default) lives in examples/bot.py:

cp .env.example .env   # fill in SLNG_API_KEY and OPENAI_API_KEY
uv run --extra example examples/bot.py

Then open http://localhost:7860/client in your browser and start talking. Pick models with SLNG_STT_MODEL / SLNG_TTS_MODEL (both default to slng/... self-hosted routes); set SLNG_PROVIDER_KEY to your own provider key to run an external route in BYOK mode. The bot uses the SmallWebRTC transport by default; pass -t daily to use Daily instead (requires installing pipecat-ai[daily]).

Development

uv sync --all-extras
uv run pytest          # unit tests (live smoke tests skip without SLNG_API_KEY)
uv run ruff check .
uv run ty check .

About SLNG

SLNG (https://slng.ai) is a unified voice AI gateway. Learn more in the SLNG docs.

License

BSD-2-Clause — see LICENSE.