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Synchronous Requests API | fal.ai Reference

While our Queue system is the more reliable and recommended way to submit requests, we also support synchronous requests via https://fal.run.

Synchronous endpoints are beneficial if when you know the request is quick and you are looking for minimal latency. The drawbacks are:

  • You need to keep the connection open until receiving the result
  • The request cannot be interrupted
  • If the connection is interrupted there is not way to obtain the result
  • You will be charged for the full request whether or not you were able to receive the result

The endpoint format and parameters are similar to the Queue ones:

EndpointMethodDescription
https://fal.run/{model_id}POSTAdds a request to the queue for a top-level path
https://fal.run/{model_id}/{subpath}POSTAdds a request to the queue for an optional subpath

Parameters:

  • model_id: the model ID consists of a namespace and model name separated by a slash, e.g. fal-ai/fast-sdxl. Many models expose only a single top-level endpoint, so you can directly call them by model_id.
  • subpath: some models expose different capabilities at different sub-paths, e.g. fal-ai/flux/dev. The subpath (/dev in this case) should be used

Submit a request

Here is an example of using the curl command to submit a synchronous request:

Terminal window
curl -X POST https://fal.run/fal-ai/fast-sdxl \
  -H "Authorization: Key $FAL_KEY" \
  -d '{"prompt": "a cat"}'

The response will come directly from the model:

{
  "images": [
    {
      "url": "https://v3.fal.media/files/rabbit/YYbm6L3DaXYHDL1_A4OaL.jpeg",
      "width": 1024,
      "height": 1024,
      "content_type": "image/jpeg"
    }
  ],
  "timings": {
    "inference": 2.507048434985336
  },
  "seed": 15860307465884635512,
  "has_nsfw_concepts": [
    false
  ],
  "prompt": "a cat"
}