Model selection - AssemblyAI

The speech_models parameter lets you specify which model(s) to use for transcription. If omitted, it defaults to ["universal-3-5-pro", "universal-2"]. With this default, universal-3-5-pro handles its 18 supported languages; for all other languages, the request will automatically fall back to universal-2.

Available models

Python SDK
JavaScript SDK
API

Name	Parameter	Description	Best for
Universal-3.5 Pro Recommended	`speech_models=['universal-3-5-pro']`	Our highest accuracy, fastest model with 18-language support, native code switching, and contextual prompting.	Highest-accuracy transcription, post-call analytics, meeting notetakers, medical transcription, domain-specific accuracy via prompting
Universal-2	`speech_models=['universal-2']`	Our accurate, cost-effective model with support across 99 languages.	High-volume batch transcription, 99-language coverage, price-sensitive workloads, fallback for unsupported U3 Pro languages

Name	Parameter	Description	Best for
Universal-3.5 Pro Recommended	`speech_models: ['universal-3-5-pro']`	Our highest accuracy, fastest model with 18-language support, native code switching, and contextual prompting.	Highest-accuracy transcription, post-call analytics, meeting notetakers, medical transcription, domain-specific accuracy via prompting
Universal-2	`speech_models: ['universal-2']`	Our accurate, cost-effective model with support across 99 languages.	High-volume batch transcription, 99-language coverage, price-sensitive workloads, fallback for unsupported U3 Pro languages

Name	API Parameter	Description	Best for
Universal-3.5 Pro Recommended	`"speech_models": ["universal-3-5-pro"]`	Our highest accuracy, fastest model with 18-language support, native code switching, and contextual prompting.	Highest-accuracy transcription, post-call analytics, meeting notetakers, medical transcription, domain-specific accuracy via prompting
Universal-2	`"speech_models":["universal-2"]`	Our accurate, cost-effective model with support across 99 languages.	High-volume batch transcription, 99-language coverage, price-sensitive workloads, fallback for unsupported U3 Pro languages

Set the model

Python
Python SDK
JavaScript
JavaScript SDK

You can change the model by setting the speech_models in the POST request body:

import requests
import time

base_url = "https://api.assemblyai.com"

headers = {
    "authorization": "<YOUR_API_KEY>"
}

data = {
    "audio_url": "https://assembly.ai/wildfires.mp3",
    "speech_models": ["universal-3-5-pro"],
    "language_detection": True
}

url = base_url + "/v2/transcript"
response = requests.post(url, json=data, headers=headers)

transcript_id = response.json()['id']
polling_endpoint = base_url + "/v2/transcript/" + transcript_id

while True:
  transcription_result = requests.get(polling_endpoint, headers=headers).json()

  if transcription_result['status'] == 'completed':
    print(transcription_result['text'])
    break

  elif transcription_result['status'] == 'error':
    raise RuntimeError(f"Transcription failed: {transcription_result['error']}")

  else:
    time.sleep(3)

You can change the model by setting speech_models in the transcription config:

import assemblyai as aai

aai.settings.api_key = "<YOUR_API_KEY>"

audio_file = "https://assembly.ai/wildfires.mp3"

config = aai.TranscriptionConfig(
    speech_models=["universal-3-5-pro"],
    language_detection=True
)
transcript = aai.Transcriber(config=config).transcribe(audio_file)

if transcript.status == aai.TranscriptStatus.error:
  raise RuntimeError(f"Transcription failed: {transcript.error}")

print(transcript.text)

You can change the model by setting the speech_models in the POST request body:

const baseUrl = "https://api.assemblyai.com";

const headers = {
  authorization: "<YOUR_API_KEY>",
};

const data = {
  audio_url: "https://assembly.ai/wildfires.mp3",
  speech_models: ["universal-3-5-pro"],
  language_detection: true,
};

const url = `${baseUrl}/v2/transcript`;
let res = await fetch(url, {
  method: "POST",
  headers: { ...headers, "Content-Type": "application/json" },
  body: JSON.stringify(data),
});
if (!res.ok) throw new Error(`Error: ${res.status}`);
const response = await res.json();

const transcriptId = response.id;
const pollingEndpoint = `${baseUrl}/v2/transcript/${transcriptId}`;

while (true) {
  res = await fetch(pollingEndpoint, { headers });
  if (!res.ok) throw new Error(`Error: ${res.status}`);
  const transcriptionResult = await res.json();

  if (transcriptionResult.status === "completed") {
    console.log(transcriptionResult.text);
    break;
  } else if (transcriptionResult.status === "error") {
    throw new Error(`Transcription failed: ${transcriptionResult.error}`);
  } else {
    await new Promise((resolve) => setTimeout(resolve, 3000));
  }
}

You can change the model by setting the speech_models in the transcript parameters:

import { AssemblyAI } from "assemblyai";

const client = new AssemblyAI({
  apiKey: "<YOUR_API_KEY>",
});

const audioFile = "https://assembly.ai/wildfires.mp3";

const params = {
  audio: audioFile,
  speech_models: ["universal-3-5-pro"],
  language_detection: true,
};

const run = async () => {
  const transcript = await client.transcripts.transcribe(params);

  if (transcript.status === "error") {
    throw new Error(`Transcription failed: ${transcript.error}`);
  }

  console.log(transcript.text);
};

run();

Identify the model used

After transcription completes, you can check which model was actually used to process your request by reading the speech_model_used field. This is useful when you provide multiple models in the speech_models array, as the system may fall back to a different model depending on language support.

Python
Python SDK
JavaScript
JavaScript SDK

import requests
import time

base_url = "https://api.assemblyai.com"

headers = {
    "authorization": "<YOUR_API_KEY>"
}

data = {
    "audio_url": "https://assembly.ai/wildfires.mp3",
    "speech_models": ["universal-3-5-pro"],
    "language_detection": True
}

url = base_url + "/v2/transcript"
response = requests.post(url, json=data, headers=headers)

transcript_id = response.json()['id']
polling_endpoint = base_url + "/v2/transcript/" + transcript_id

while True:
  transcription_result = requests.get(polling_endpoint, headers=headers).json()

  if transcription_result['status'] == 'completed':
    print(f"Model used: {transcription_result['speech_model_used']}")
    print(transcription_result['text'])
    break

  elif transcription_result['status'] == 'error':
    raise RuntimeError(f"Transcription failed: {transcription_result['error']}")

  else:
    time.sleep(3)

import assemblyai as aai

aai.settings.api_key = "<YOUR_API_KEY>"

audio_file = "https://assembly.ai/wildfires.mp3"

config = aai.TranscriptionConfig(
    speech_models=["universal-3-5-pro"],
    language_detection=True
)
transcript = aai.Transcriber(config=config).transcribe(audio_file)

if transcript.status == aai.TranscriptStatus.error:
    raise RuntimeError(f"Transcription failed: {transcript.error}")

print(f"Model used: {transcript.json_response['speech_model_used']}")
print(transcript.text)

const baseUrl = "https://api.assemblyai.com";

const headers = {
  authorization: "<YOUR_API_KEY>",
};

const data = {
  audio_url: "https://assembly.ai/wildfires.mp3",
  speech_models: ["universal-3-5-pro"],
  language_detection: true,
};

const url = `${baseUrl}/v2/transcript`;
let res = await fetch(url, {
  method: "POST",
  headers: { ...headers, "Content-Type": "application/json" },
  body: JSON.stringify(data),
});
if (!res.ok) throw new Error(`Error: ${res.status}`);
const response = await res.json();

const transcriptId = response.id;
const pollingEndpoint = `${baseUrl}/v2/transcript/${transcriptId}`;

while (true) {
  res = await fetch(pollingEndpoint, { headers });
  if (!res.ok) throw new Error(`Error: ${res.status}`);
  const transcriptionResult = await res.json();

  if (transcriptionResult.status === "completed") {
    console.log(`Model used: ${transcriptionResult.speech_model_used}`);
    console.log(transcriptionResult.text);
    break;
  } else if (transcriptionResult.status === "error") {
    throw new Error(`Transcription failed: ${transcriptionResult.error}`);
  } else {
    await new Promise((resolve) => setTimeout(resolve, 3000));
  }
}

import { AssemblyAI } from "assemblyai";

const client = new AssemblyAI({
  apiKey: "<YOUR_API_KEY>",
});

const audioFile = "https://assembly.ai/wildfires.mp3";

const params = {
  audio: audioFile,
  speech_models: ["universal-3-5-pro"],
  language_detection: true,
};

const run = async () => {
  const transcript = await client.transcripts.transcribe(params);

  if (transcript.status === "error") {
    throw new Error(`Transcription failed: ${transcript.error}`);
  }

  console.log(`Model used: ${transcript.speech_model_used}`);
  console.log(transcript.text);
};

run();

Complete example

Here is the full working code that demonstrates model selection with error handling:

Python
Python SDK
JavaScript
JavaScript SDK

import requests
import time

base_url = "https://api.assemblyai.com"
headers = {"authorization": "<YOUR_API_KEY>"}

data = {
    "audio_url": "https://assembly.ai/wildfires.mp3",
    "speech_models": ["universal-3-5-pro"],
    "language_detection": True
}

response = requests.post(base_url + "/v2/transcript", headers=headers, json=data)

if response.status_code != 200:
    print(f"Error: {response.status_code}, Response: {response.text}")
    response.raise_for_status()

transcript_json = response.json()
transcript_id = transcript_json["id"]
polling_endpoint = f"{base_url}/v2/transcript/{transcript_id}"

while True:
    transcript = requests.get(polling_endpoint, headers=headers).json()
    if transcript["status"] == "completed":
        print(f"Model used: {transcript['speech_model_used']}")
        print(f"\nTranscript:\n\n{transcript['text']}")
        break
    elif transcript["status"] == "error":
        raise RuntimeError(f"Transcription failed: {transcript['error']}")
    else:
        time.sleep(3)

import assemblyai as aai

aai.settings.api_key = "<YOUR_API_KEY>"

audio_file = "https://assembly.ai/wildfires.mp3"

config = aai.TranscriptionConfig(
    speech_models=["universal-3-5-pro"],
    language_detection=True,
)

transcript = aai.Transcriber(config=config).transcribe(audio_file)

if transcript.status == aai.TranscriptStatus.error:
    raise RuntimeError(f"Transcription failed: {transcript.error}")

print(f"Model used: {transcript.json_response['speech_model_used']}")
print(f"\nTranscript:\n\n{transcript.text}")

const baseUrl = "https://api.assemblyai.com";

const headers = {
  authorization: "<YOUR_API_KEY>",
};

async function transcribe() {
  const audioFile = "https://assembly.ai/wildfires.mp3";

  const data = {
    audio_url: audioFile,
    speech_models: ["universal-3-5-pro"],
    language_detection: true,
  };

  let res = await fetch(`${baseUrl}/v2/transcript`, {
    method: "POST",
    headers: { ...headers, "Content-Type": "application/json" },
    body: JSON.stringify(data),
  });
  if (!res.ok) throw new Error(`Error: ${res.status}`);
  const transcriptResponse = await res.json();
  const transcriptId = transcriptResponse.id;
  const pollingEndpoint = `${baseUrl}/v2/transcript/${transcriptId}`;

  while (true) {
    res = await fetch(pollingEndpoint, { headers });
    if (!res.ok) throw new Error(`Error: ${res.status}`);
    const transcript = await res.json();

    if (transcript.status === "completed") {
      console.log(`Model used: ${transcript.speech_model_used}`);
      console.log(`\nTranscript:\n\n${transcript.text}`);
      break;
    } else if (transcript.status === "error") {
      throw new Error(`Transcription failed: ${transcript.error}`);
    } else {
      await new Promise((resolve) => setTimeout(resolve, 3000));
    }
  }
}

transcribe();

import { AssemblyAI } from "assemblyai";

const client = new AssemblyAI({
  apiKey: "<YOUR_API_KEY>",
});

const audioFile = "https://assembly.ai/wildfires.mp3";

const params = {
  audio: audioFile,
  speech_models: ["universal-3-5-pro"],
  language_detection: true,
};

const run = async () => {
  const transcript = await client.transcripts.transcribe(params);

  if (transcript.status === "error") {
    throw new Error(`Transcription failed: ${transcript.error}`);
  }

  console.log(`Model used: ${transcript.speech_model_used}`);
  console.log(`\nTranscript:\n\n${transcript.text}`);
};

run();

​Available models

​Set the model

​Identify the model used

​Complete example

Available models

Set the model

Identify the model used

Complete example