Pixazo API→Models→Speech to Text API→AssemblyAI

AssemblyAI Universal 3 Pro API: Pricing, Documentation

AssemblyAI's Universal 3 Pro speech recognition. Returns the transcript with per-word timings, per-utterance segmentation and a confidence score, plus the detected language.

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AssemblyAI Universal 3 Pro API Documentation

AssemblyAI's Universal 3 Pro. Returns the transcript with per-word timings, per-utterance segmentation and a confidence score, plus the detected language. Asynchronous: submit returns a request_id; poll the status endpoint until the request is COMPLETED, then download the audio.

POST https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text

Authentication

All requests require an API key passed via header.

Header	Type	Required	Description
Ocp-Apim-Subscription-Key	string	Yes	Your API subscription key

Speech to Text - AssemblyAI Universal 3 Pro

Request Code

POST https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text
Content-Type: application/json
Ocp-Apim-Subscription-Key: YOUR_SUBSCRIPTION_KEY

{
  "audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"
}

import requests

url = "https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text"
headers = {
    "Content-Type": "application/json",
    "Ocp-Apim-Subscription-Key": "YOUR_SUBSCRIPTION_KEY"
}
data = {
  "audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"
}

resp = requests.post(url, json=data, headers=headers)
print(resp.json())

const res = await fetch("https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Ocp-Apim-Subscription-Key": "YOUR_SUBSCRIPTION_KEY"
  },
  body: JSON.stringify({
  "audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"
})
});
console.log(await res.json());

curl -X POST 'https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text' \
  -H 'Content-Type: application/json' \
  -H 'Ocp-Apim-Subscription-Key: YOUR_SUBSCRIPTION_KEY' \
  --data-raw '{"audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"}'

Output

{
  "request_id": "assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "status": "QUEUED",
  "polling_url": "https://gateway.pixazo.ai/v2/requests/status/assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
}

Try Now

Webhook (Optional)

Instead of polling, you can receive a Webhook callback when the request reaches a terminal state. Provide a Webhook URL via header on the submit request.

Header	Required	Description
X-Webhook-URL	To enable	HTTPS URL to receive the Webhook callback.
X-Webhook-Mode	No	`terminal` (default, one callback on COMPLETED/ERROR) or `sync` (per-poll callbacks).

Example: enable Webhook

curl -X POST 'https://gateway.pixazo.ai/assemblyai-universal-3-pro/v1/speech-to-text' \
  -H 'Content-Type: application/json' \
  -H 'Ocp-Apim-Subscription-Key: YOUR_SUBSCRIPTION_KEY' \
  -H 'X-Webhook-URL: https://your-server.com/webhook' \
  --data-raw '{"audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"}'

Callback Payload (success)

{
  "request_id": "assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "status": "COMPLETED",
  "model_id": "assemblyai-universal-3-pro",
  "output": {
    "media_url": [
      "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/v1/{request_id}/transcript.json"
    ],
    "media_type": "application/json"
  },
  "duration": 19.17,
  "created_at": "2026-08-01T09:14:16.102Z",
  "completed_at": "2026-08-01T09:14:22.870Z"
}

Failure callback shape

{
  "request_id": "assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "status": "ERROR",
  "model_id": "assemblyai-universal-3-pro",
  "error": "Description of the failure"
}

Delivery semantics

terminal mode: one Webhook callback when the request is COMPLETED or ERROR.
sync mode: a Webhook callback on each status change.
Callbacks are idempotent on request_id — de-duplicate on it.
Respond 200 within a few seconds; the Webhook endpoint must be HTTPS.

Request Parameters

Parameter	Required	Type	Default	Allowed values / range	Description
`audio_url`	Yes	string	—	a publicly reachable http(s) url	The recording to transcribe. We fetch it server-side, so it must be reachable from the internet — a signed url is fine, a private one is not. `audio` is accepted as an alias.
`language`	No	string	—	ISO 639-1, e.g. `en`	Omit this to let the model detect the language — that is the default. `auto` means the same. Set it to force one of the recording.
`prompt`	No	string	—	up to 2,000 characters	Bias the transcription toward expected wording — names, jargon, spellings.

Voices

Word timings are returned in milliseconds. Utterances group the transcript into speaker turns.

Example Request

{
  "audio_url": "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/doc-assets/audio/speech-17s.mp3"
}

Example Response

{
  "request_id": "assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "status": "QUEUED",
  "polling_url": "https://gateway.pixazo.ai/v2/requests/status/assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
}

Request Headers

Header	Required	Description
Content-Type	Yes	`application/json`
Ocp-Apim-Subscription-Key	Yes	Your API subscription key.
X-Webhook-URL	No	Enable Webhook callbacks (see Webhook section).

Response Handling

Status Code	Meaning
202	Accepted — request queued; returns `request_id` and `polling_url`.
400	Bad request — a missing or out-of-range parameter. The message names the field.
401	Unauthorized — missing or invalid subscription key.
402	Insufficient balance.
429	Too many requests.
500	Internal server error.

Retrieving Results

Poll the status endpoint with the request_id from the submit response until status is COMPLETED (or ERROR), then download output.media_url.

curl 'https://gateway.pixazo.ai/v2/requests/status/assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx' \
  -H 'Ocp-Apim-Subscription-Key: YOUR_SUBSCRIPTION_KEY'

Completed response

{
  "request_id": "assemblyai-universal-3-pro_019dxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "status": "COMPLETED",
  "model_id": "assemblyai-universal-3-pro",
  "output": {
    "media_url": [
      "https://pub-582b7213209642b9b995c96c95a30381.r2.dev/v1/{request_id}/transcript.json"
    ],
    "media_type": "application/json"
  },
  "duration": 19.17,
  "created_at": "2026-08-01T09:14:16.102Z",
  "completed_at": "2026-08-01T09:14:22.870Z"
}

Response Fields

Field	Type	Description
request_id	string	Unique request identifier.
status	string	QUEUED, PROCESSING, COMPLETED or ERROR.
model_id	string	The model that handled the request.
output.media_url	array	URL of the generated audio file.
output.media_type	string	MIME type of the audio.
created_at	string	Request creation timestamp.
completed_at	string	Completion timestamp.
error	string	Error message when `status` is ERROR.

Status Values & Flow

QUEUED → PROCESSING → COMPLETED (success) or ERROR (failure).

Pricing

Billed at $0.0035 per minute of generated audio, rounded up to the next whole minute. You are charged for the audio produced, not the text you submit.

Audio produced	Billed minutes	Cost
A 10-second clip	1	$0.0035
A 45-second clip	1	$0.0035
A 3-minute narration	3	$0.0105
A 10-minute narration	10	$0.035

Failed requests are not billed.

AssemblyAI Universal 3 Pro API Pricing

Your request will cost $0.0035 per minute of audio transcribed.

an hour of audio is $0.21

equivalent to $0.21 per hour of audio

⚡ Performance

Live usage measured on Pixazo's gateway, split by model version. Generation time is how long a generation takes end-to-end (lower is better). Success rate is the percent of generations that complete (higher is better).

Show data for the last

Generations

100last 30d

~3 per day

Success rate

100.0%

of completed generations

Generation time

82.8savg

p95 82.8s

Requests

Jul 16max 100Aug 14

AssemblyAI Universal 3 ProAvg 3/day

Generation Time

Jul 16max 82.8sAug 14

AssemblyAI Universal 3 ProAvg 82.8s

Error Rate

Jul 16max 5.0%Aug 14

AssemblyAI Universal 3 ProAvg 0.0%

〰 Uptime

Percent of generations that succeeded over the selected period, per model version.

Avg. Success Rate (30d)

100.00%

across all generations of this model family

Uptime

Jul 16max 100%Aug 14

SuccessfulAvg 100.00%