Text-to-Audio Generation API

Generate music and soundscapes from natural-language text prompts using FastRouter’s text-to-audio model routing.

Introduction

FastRouter.ai integrates the ace-step/prompt-to-audio model from the falai provider, enabling developers to turn prompts into fully rendered audio clips for creative, musical, or ambient use cases.

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Endpoints

Audio Generation

POST https://go.fastrouter.ai/api/v1/chat/completions

Retrieve Generated Audio

POST https://go.fastrouter.ai/api/v1/getPromptToAudioResponse

Base URL

https://go.fastrouter.ai/api/v1

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Parameters

Parameter	Type	Description
model	string	Must be "ace-step/prompt-to-audio"
prompt	string	Natural-language description of the audio or music to generate
duration	integer	(Optional) Duration of the audio clip in seconds (e.g. 5)

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Request Format

Send a natural-language prompt to generate audio, optionally specifying a duration.

cURL Example

curl --location 'https://go.fastrouter.ai/api/v1/chat/completions' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "ace-step/prompt-to-audio",
    "prompt": "A lofi hiphop song with a chill vibe about a sunny day on the boardwalk.",
    "duration": 5
}'

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Python Example

import requests

url = "https://go.fastrouter.ai/api/v1/chat/completions"
headers = {
    "Authorization": "Bearer API-KEY",
    "Content-Type": "application/json"
}

payload = {
    "model": "ace-step/prompt-to-audio",
    "prompt": "Ambient forest background sound with soft wind and birds chirping.",
    "duration": 8
}

response = requests.post(url, json=payload, headers=headers)
print(response.json())

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Sample Response

FastRouter returns a job-queued response containing URLs to check status or fetch the final audio file:

{
  "chat_id": "fr_12345",
  "model": "ace-step/prompt-to-audio",
  "status": "IN_QUEUE",
  "request_id": "123abcdef",
  "response_url": "https://queue.fal.run/fal-ai/ace-step/requests/123abcdef",
  "status_url": "https://queue.fal.run/fal-ai/ace-step/requests/123abcdef/status",
  "cancel_url": "https://queue.fal.run/fal-ai/ace-step/requests/123abcdef/cancel",
  "logs": null,
  "queue_position": 0,
  "usage": {
    "chat_id": "fr_12345",
    "prompt_tokens": 0,
    "completion_tokens": 0,
    "total_tokens": 0,
    "user_key_credits_used": 0.025,
    "credits_used": 0.025,
    "provider": "falai"
  }
}

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Retrieving the Audio Output

Audio generation is asynchronous. Use the response_url returned above with this FastRouter endpoint to retrieve the final audio.

Polling for Audio Output (cURL)

curl --location 'https://go.fastrouter.ai/api/v1/getPromptToAudioResponse' \
--header 'Authorization: Bearer API-KEY' \
--data '{
    "url": "https://queue.fal.run/fal-ai/ace-step/requests/123abcdef",
    "model": "ace-step/prompt-to-audio"
}'

When complete, the response includes a downloadable .wav or .mp3 audio link.

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Billing & Usage

• Credits used: See user_key_credits_used in the usage object

• Costs: Based on clip duration + model pricing

• No hidden charges: Transparent usage reporting in all responses