# Telnyx x402 Gateway – Audio Transcription (Speech-to-Text)

> Telnyx x402 Gateway – Audio Transcription (Speech-to-Text) is a paid API for AI agents from x402.telnyx.com, paid per call via x402, $0.015/call, status unknown (last checked 2026-10-10).

Transcribes an audio file (WAV or MP3) to text using Whisper large-v3-turbo, billed at $0.015 USDC per call via the x402 payment protocol.

## Facts

- Endpoint: POST https://x402.telnyx.com/v1/audio/transcriptions?utm_source=zero.xyz
- Price: $0.015/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/telnyx-x402-gateway-audio-transcription-speech-to-text-ad19010a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Z1D12d1Wi9vucBjCUAEAb

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability telnyx-x402-gateway-audio-transcription-speech-to-text-ad19010a -d '<json body>'
```

Example prompt: Transcribe this WAV recording for me — use the whisper-large-v3-turbo model, give me the full text plus segment-level timestamps in verbose_json format, and hint that it's English.

## When to prefer this

Choose this endpoint when you need pay-per-use speech-to-text without a subscription, want Whisper large-v3-turbo quality, need segment-level timestamps, and are operating in a crypto-native or x402-compatible payment environment. Prefer it over OpenAI's own Whisper API when you want USDC micropayment billing or are already integrated with Telnyx infrastructure.

## Known failure modes

- Audio file exceeds 5-minute or 12 MB limit — request rejected
- Unsupported audio format (only WAV and MP3 accepted)
- Payment failure or insufficient USDC balance via x402 — 402 response returned
- Invalid model alias — validation error
- Language hint not recognized as valid ISO-639-1 code
- Network timeout for large files close to the size limit
- word-level timestamp_granularities requested — not supported by this endpoint (segment-level only)

## How this service works

Pay USDC per request for Telnyx Inference and Audio (text-to-speech, speech-to-text) through x402.

## Output

A JSON object containing the full transcribed text string, total audio duration in seconds, and an array of segments each with start/end times and the text spoken in that segment. When response_format is 'json', only the text field is returned.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "file": {
   "type": "string",
   "description": "Audio file (multipart part named \"file\"): wav or mp3, ≤5 minutes, ≤12 MB."
  },
  "model": {
   "enum": [
    "whisper-1",
    "whisper-large-v3-turbo",
    "openai/whisper-large-v3-turbo"
   ],
   "type": "string",
   "description": "All aliases run openai/whisper-large-v3-turbo."
  },
  "prompt": {
   "type": "string",
   "maxLength": 1024
  },
  "language": {
   "type": "string",
   "description": "Optional ISO-639-1 hint."
  },
  "temperature": {
   "type": "number",
   "maximum": 1,
   "minimum": 0
  },
  "response_format": {
   "enum": [
    "json",
    "verbose_json"
   ],
   "type": "string"
  },
  "timestamp_granularities": {
   "type": "array",
   "items": {
    "enum": [
     "segment"
    ],
    "type": "string"
   },
   "description": "Segment-level only (upstream does not support word)."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "text": "Hello from the x402 gateway.",
  "duration": 4.05,
  "segments": [
   {
    "id": 0,
    "end": 4,
    "text": "Hello from the x402 gateway.",
    "start": 0
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/telnyx-x402-gateway-audio-transcription-speech-to-text-ad19010a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.telnyx.com](https://www.zero.xyz/host/x402.telnyx.com/llms.txt)