BYOK Voice Models

This page covers passing your own key per request when you call the speech APIs directly. For managed voice agents, register org-level BYOK models in the Dashboard instead — see Bring Your Own Key.

If you already have a contract with a text-to-speech provider, you can keep it. Bring Your Own Key (BYOK) lets you pass your own provider key on requests. Your key is forwarded upstream, so billing and rate limits run against your provider account, and TTS Path Optimization still applies on top.

Placeholders

The snippets below use these placeholders. Replace them before running the code.

Placeholder	Replace with
`SLNG_API_KEY`	An SLNG key from app.slng.ai/api-keys
`YOUR_PROVIDER_KEY`	A provider key issued by the upstream TTS provider you are calling

How Path Optimization applies

TTS path optimization runs before your request is forwarded, so a cache hit never reaches the upstream provider:

Cache hit: the cached audio is returned, no provider call, and no billing event.
Cache miss: the request is sent upstream with your key, the provider bills your account, and the response is cached for future requests.

Supported providers

Provider	Model
Cartesia	Sonic 3
Deepgram	Aura 2
Kugel	Kugel 1 Turbo, Kugel 1, Kugel 2
Murf	Falcon
Sarvam	Bulbul
Soniox	TTS RT v1
Gradium	Gradium TTS v1

Send a BYOK request

Add the X-Slng-Provider-Key header alongside your standard SLNG Authorization header.

HTTP

curl -X POST "https://api.slng.ai/v1/tts/sarvam/bulbul:v3" \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -H "X-Slng-Provider-Key: YOUR_PROVIDER_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "I brought my own key to the party.",
    "target_language_code": "en-IN",
    "speaker": "shubh",
    "model": "bulbul:v3"
  }'

WebSocket

Set X-Slng-Provider-Key as a header on the WebSocket upgrade request. The message flow after the upgrade is unchanged.

X-Slng-Provider-Key: YOUR_PROVIDER_KEY

The browser WebSocket API does not support custom headers. Set the provider key from a server-side WebSocket client.

Error handling

HTTP

If the upstream provider rejects your key, the provider’s error response is returned with this header:

X-Slng-Auth-Source: client_key

That header tells you the failure came from your provider key, not from SLNG.

WebSocket

Auth failures surface as a WebSocket error frame after the upgrade is accepted, for example backend_connection_failed, with the upstream 401 or 403 detail included.

Overview

Pipeline

Context Router

TTS path Optimization

Placeholders

How Path Optimization applies

Supported providers

Send a BYOK request

HTTP

WebSocket

Error handling

HTTP

WebSocket

Next steps

Pronunciation Dictionaries

Drop-in gateway

​Placeholders

​How Path Optimization applies

​Supported providers

​Send a BYOK request

​HTTP

​WebSocket

​Error handling

​HTTP

​WebSocket

​Next steps

Pronunciation Dictionaries

Drop-in gateway

Placeholders

How Path Optimization applies

Supported providers

Send a BYOK request

HTTP

WebSocket

Error handling

HTTP

WebSocket

Next steps