Queue API | fal.ai Reference

For requests that take longer than several seconds, as it is usually the case with AI models, we provide a queue system.

It offers granular control in dealing with surges in traffic, allows you to cancel requests and monitor the current position within the queue, and removes the need to keep long running connections open.

Queue endpoints

The queue functionality is exposed via standardized per-model paths under https://queue.fal.run.

Endpoint	Method	Description
https://queue.fal.run/{model_id}	POST	Adds a request to the queue for a top-level path
https://queue.fal.run/{model_id}/{subpath}	POST	Adds a request to the queue for an optional subpath
https://queue.fal.run/{model_id}/requests/{request_id}/status	GET	Gets the status of a request
https://queue.fal.run/{model_id}/requests/{request_id}/status/stream	GET	Streams the status of a request until it’s completed
https://queue.fal.run/{model_id}/requests/{request_id}	GET	Gets the response of a request
https://queue.fal.run/{model_id}/requests/{request_id}/cancel	PUT	Cancels a request that has not started processing

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 when making the request, but not when getting request status or results
• request_id is returned after adding a request to the queue. This is the identifier you use to check the status and get results and logs

Submit a request

Here is an example of using curl to submit a request which will add it to the queue:

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

Here’s an example of a response with the request_id:

{
  "request_id": "80e732af-660e-45cd-bd63-580e4f2a94cc",
  "response_url": "https://queue.fal.run/fal-ai/fast-sdxl/requests/80e732af-660e-45cd-bd63-580e4f2a94cc",
  "status_url": "https://queue.fal.run/fal-ai/fast-sdxl/requests/80e732af-660e-45cd-bd63-580e4f2a94cc/status",
  "cancel_url": "https://queue.fal.run/fal-ai/fast-sdxl/requests/80e732af-660e-45cd-bd63-580e4f2a94cc/cancel"
}

The payload helps you to keep track of your request with the request_id, and provides you with the necessary information to get the status of your request, cancel it or get the response once it’s ready, so you don’t have to build these endpoints yourself.

Request status

Once you have the request id you may use this request id to get the status of the request. This endpoint will give you information about your request’s status, it’s position in the queue or the response itself if the response is ready.

curl -X GET https://queue.fal.run/fal-ai/fast-sdxl/requests/{request_id}/status

Here’s an example of a response with the IN_QUEUE status:

{
  "status": "IN_QUEUE",
  "queue_position": 0,
  "response_url": "https://queue.fal.run/fal-ai/fast-sdxl/requests/80e732af-660e-45cd-bd63-580e4f2a94cc"
}

Status types

Queue status can have one of the following types and their respective properties:

• IN_QUEUE:

  • queue_position: The current position of the task in the queue.
  • response_url: The URL where the response will be available once the task is processed.

• IN_PROGRESS:

  • logs: An array of logs related to the request. Note that it needs to be enabled, as explained in the next section.
  • response_url: The URL where the response will be available.

• COMPLETED:

  • logs: An array of logs related to the request. Note that it needs to be enabled, as explained in the next section.
  • response_url: The URL where the response is available.

Logs

Logs are disabled by default. In order to enable logs for your request, you need to send the logs=1 query parameter when getting the status of your request. For example:

curl -X GET https://queue.fal.run/fal-ai/fast-sdxl/requests/{request_id}/status?logs=1

When enabled, the logs attribute in the queue status contains an array of log entries, each represented by the RequestLog type. A RequestLog object has the following attributes:

• message: a string containing the log message.
• level: the severity of the log, it can be one of the following:
  • STDERR | STDOUT | ERROR | INFO | WARN | DEBUG
• source: indicates the source of the log.
• timestamp: a string representing the time when the log was generated.

These logs offer valuable insights into the status and progress of your queued tasks, facilitating effective monitoring and debugging.

Streaming status

If you want to keep track of the status of your request in real-time, you can use the streaming endpoint. The response is text/event-stream and each event is a JSON object with the status of the request exactly as the non-stream endpoint.

This endpoint will keep the connection open until the status of the request changes to COMPLETED.

It supports the same logs query parameter as the status.

curl -X GET https://queue.fal.run/fal-ai/fast-sdxl/requests/{request_id}/status/stream

Here is an example of a stream of status updates:

$ curl https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status/stream?logs=1 --header "Authorization: Key $FAL_KEY"

data: {"status": "IN_PROGRESS", "request_id": "3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "response_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "status_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status", "cancel_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/cancel", "logs": [], "metrics": {}}

data: {"status": "IN_PROGRESS", "request_id": "3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "response_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "status_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status", "cancel_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/cancel", "logs": [{"timestamp": "2024-12-20T15:37:17.120314", "message": "INFO:TRYON:Preprocessing images...", "labels": {}}, {"timestamp": "2024-12-20T15:37:17.286519", "message": "INFO:TRYON:Running try-on model...", "labels": {}}], "metrics": {}}

data: {"status": "IN_PROGRESS", "request_id": "3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "response_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "status_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status", "cancel_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/cancel", "logs": [], "metrics": {}}

: ping

data: {"status": "IN_PROGRESS", "request_id": "3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "response_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "status_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status", "cancel_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/cancel", "logs": [], "metrics": {}}

data: {"status": "COMPLETED", "request_id": "3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "response_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf", "status_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/status", "cancel_url": "https://queue.fal.run/fashn/tryon/requests/3e3e5b55-45fb-4e5c-b4d1-05702dffc8bf/cancel", "logs": [{"timestamp": "2024-12-20T15:37:32.161184", "message": "INFO:TRYON:Finished running try-on model.", "labels": {}}], "metrics": {"inference_time": 17.795265674591064}}

Cancelling a request

If your request has not started processing (status is IN_QUEUE), you may attempt to cancel it.

curl -X PUT https://queue.fal.run/fal-ai/fast-sdxl/requests/{request_id}/cancel

If the request has not already started processing, you will get a 202 Accepted response with the following body:

{
  "status": "CANCELLATION_REQUESTED"
}

Note that a request may still be executed after getting this response if it was very late in the queue process.

If the request is already processed, you will get a 400 Bad Request response with this body:

{
  "status": "ALREADY_COMPLETED"
}

Getting the response

Once you get the COMPLETED status, the response will be available along with its logs.

curl -X GET https://queue.fal.run/fal-ai/fast-sdxl/requests/{request_id}

Here’s an example of a response with the COMPLETED status:

{
  "status": "COMPLETED",
  "logs": [
    {
      "message": "2020-05-04 14:00:00.000000",
      "level": "INFO",
      "source": "stdout",
      "timestamp": "2020-05-04T14:00:00.000000Z"
    }
  ],
  "response": {
    "message": "Hello World!"
  }
}

A simple queue recipe

Submit your request and let our client handle the status tracking for you. The next section details how the fal client simplifies building apps with fal functions.

Using webhook callbacks

Instead of polling for the request status, you can have fal call a webhook when a request is finished. Please refer to the Webhooks page.