Stream speech to text over WebSocket

AsyncAPI specification for the Telnyx Speech-to-Text WebSocket endpoint. Real-time speech transcription by streaming audio and receiving transcript frames.

Supported Engines

Azure - Microsoft Azure Speech Services
Deepgram - Deepgram Nova and Flux models
Google - Google Cloud Speech-to-Text
Telnyx - Telnyx native transcription (OpenAI Whisper models)
xAI - xAI Grok STT
AssemblyAI - AssemblyAI Universal-Streaming (backed by Universal-3.5 Pro Realtime)
Speechmatics - Speechmatics real-time transcription
Soniox - Soniox real-time transcription
Parakeet - Self-hosted NVIDIA Parakeet multilingual transcription
Reson8 - Reson8 turn-based multilingual transcription
Cohere - Self-hosted Cohere Arabic/English transcription (batch, no auto-detect)

Connection Flow

Open WebSocket connection to wss://api.telnyx.com/v2/speech-to-text/transcription with query parameters.
Send binary audio frames (mp3, wav, linear16, or linear32 format, per input_format).
Receive JSON transcript frames with transcript, is_final, and confidence fields.
Close connection when done.

Authentication

Requires authentication via a Bearer token (Telnyx API v2 key).

WSS

speech-to-text

transcription

Messages

bearerAuth

type:http

Telnyx API v2 Bearer token authentication.

query

type:object

Query parameters passed when opening the WebSocket connection.

Audio Frame

type:string

Client-to-server binary frame containing audio data to transcribe. Audio should be in mp3, wav, linear16, or linear32 format as specified in the input_format query parameter.

Transcript Frame

type:object

Server-to-client frame containing a transcription result. When interim_results is enabled, you may receive multiple interim results (is_final=false) before the final result (is_final=true) for each utterance.

Reson8 transcribes per turn of speech: each interim frame carries the full transcript of the turn so far and supersedes the previous frame, the final frame arrives when the turn ends, and confidence is omitted from its frames.

Error Frame

type:object

Server-to-client frame indicating an error during transcription. The connection may be closed shortly after sending this frame.

Messages

WebSocket

REST API

In-Call

For AI Agents

Stream speech to text over WebSocket

Supported Engines

Connection Flow

Authentication