SLNG Unified API

One endpoint pattern for every STT and TTS model on the platform. Switch providers by changing the URL path. Your code, auth, and request format don’t change.

Swap models by changing the URL

Every request uses the same base URL. The only part that changes is the model path:

	Base URL	Model path
Deepgram Nova 3 (proxied)	`api.slng.ai/v1/bridges/unmute/stt/`	`deepgram/nova:3`
Deepgram Nova 3 (SLNG-hosted)	`api.slng.ai/v1/bridges/unmute/stt/`	`slng/deepgram/nova:3-en`
Deepgram Aura 2	`api.slng.ai/v1/bridges/unmute/tts/`	`slng/deepgram/aura:2-en`
Rime Arcana v3	`api.slng.ai/v1/bridges/unmute/tts/`	`slng/rime/arcana:3-en`

Authentication, request body, and response format are identical. Only the path differs.

Why a unified interface

Most voice AI stacks lock you into one provider’s SDK, request format, and response structure. The Unified API removes that friction.

Without SLNG Unified API	With SLNG Unified API
One SDK per provider	One HTTP/WebSocket endpoint for all
Different request schemas	Same request body across providers
Provider-specific error handling	Consistent error responses
Weeks to evaluate a new model	Change the URL path, test immediately
Manual upgrades when better models ship	New models available as soon as SLNG adds them

Common patterns:

A/B testing: route a percentage of traffic to a different model path with no code change.
Failover: switch providers by changing the model path; request format and error handling stay the same.
Latency optimization: deploy across regions and route each one to the lowest-latency model.
Rapid prototyping: try a new model by changing the URL.

The Unified API doesn’t hide provider capabilities. Pass voice identifiers, sample rates, encodings, language codes, and speed settings through the config object. See Parameters coverage for the full list.

Works over HTTP and WebSocket

The same model path works with both protocols:

Protocol	URL
HTTP	`https://api.slng.ai/v1/bridges/unmute/tts/slng/deepgram/aura:2-en`
WebSocket	`wss://api.slng.ai/v1/bridges/unmute/tts/slng/deepgram/aura:2-en`

Use HTTP for batch jobs and file conversion. Use WebSocket for real-time streaming and voice agents. See HTTP vs. WebSocket for details.

Get started

Prerequisites

An SLNG key (get one here)
curl installed (or any HTTP client)

Authentication

All requests require a Bearer token:

Authorization: Bearer SLNG_API_KEY

Text-to-Speech

Generate speech from text. Here’s a request using Rime Arcana v3:

curl -X POST https://api.slng.ai/v1/bridges/unmute/tts/slng/rime/arcana:3-en \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "voice": "luna",
    "text": "Hello from the SLNG Unified API!"
  }' \
  --output hello.wav

This saves a WAV file. You can set encoding and sample rate through the config object. To make acronyms, product names, and domain terms speak consistently across TTS models, attach a pronunciation dictionary to the request.

The model is inferred from the URL path. Do not include a duplicate model field in the request body unless an endpoint reference explicitly requires it.

Switch to Deepgram Aura 2 by changing the URL path and adapting the voice.

curl -X POST https://api.slng.ai/v1/bridges/unmute/tts/slng/deepgram/aura:2-en \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "voice": "aura-2-asteria-en",
    "text": "Hello from the SLNG Unified API!"
  }' \
  --output hello.wav

Speech-to-Text

Transcribe audio with SLNG-hosted Deepgram Nova 3:

curl -X POST https://api.slng.ai/v1/bridges/unmute/stt/slng/deepgram/nova:3-en \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -F "audio=@recording.wav" \
  -F "language=en"

Switch to proxied Deepgram Nova 3 for 17-language coverage. Only the URL changes:

curl -X POST https://api.slng.ai/v1/bridges/unmute/stt/deepgram/nova:3 \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -F "audio=@recording.wav" \
  -F "language=en"

WebSocket streaming

The same model paths work over WebSocket for real-time streaming. Connect to wss:// instead of posting to https://.

The browser WebSocket API does not support custom headers. Pass the SLNG key as a query parameter or use a server-side WebSocket client. The example below uses the Node.js ws library.

import WebSocket from "ws";

const ws = new WebSocket(
  "wss://api.slng.ai/v1/bridges/unmute/tts/slng/deepgram/aura:2-en",
  { headers: { Authorization: "Bearer SLNG_API_KEY" } }
);

ws.on("open", () => {
  ws.send(JSON.stringify({
    voice: "aura-2-asteria-en",
    text: "Streaming audio in real time."
  }));
});

ws.on("message", (data) => {
  // Binary frames contain audio chunks
  if (Buffer.isBuffer(data)) {
    process.stdout.write(data);
  }
});

For browser-based WebSocket examples, see TTS over WebSocket.

Next steps

Parameters coverage

See which parameters each provider supports.

Supported models

Browse all models available through the Unified API.

HTTP vs. WebSocket

When to use each protocol and their trade-offs.

Overview

Pipeline

Configuration

Unified API

Swap models by changing the URL

Why a unified interface

Works over HTTP and WebSocket

Get started

Prerequisites

Authentication

Text-to-Speech

Speech-to-Text

WebSocket streaming

Next steps

Parameters coverage

Supported models

HTTP vs. WebSocket

​Swap models by changing the URL

​Why a unified interface

​Works over HTTP and WebSocket

​Get started

​Prerequisites

​Authentication

​Text-to-Speech

​Speech-to-Text

​WebSocket streaming

​Next steps

Parameters coverage

Supported models

HTTP vs. WebSocket

Swap models by changing the URL

Why a unified interface

Works over HTTP and WebSocket

Get started

Prerequisites

Authentication

Text-to-Speech

Speech-to-Text

WebSocket streaming

Next steps