Inference Methods

Learn the different ways to call models on fal

Every model on fal can be called through the same set of inference methods, whether it is a pre-trained model from the gallery or your own app running on Serverless. This page walks through each method, explains when to reach for it, and links to the deeper reference pages. Before calling any model you will need an API key and the fal client installed in your project.

fal provides five calling patterns that cover the spectrum from quick prototyping to high-throughput production pipelines. All of them benefit from fal’s autoscaling infrastructure, where runners spin up on demand to handle your requests. The key decision is whether you need the queue (recommended for reliability), a direct call (simplest path), streaming (progressive output), or a real-time WebSocket connection (lowest latency). Each method is covered below with a code example and guidance on when it is the right fit.

These calling patterns work identically for your own deployed serverless apps. Use your app’s endpoint ID (e.g., your-username/your-app-name) instead of a model ID. See Calling Your Endpoints for serverless-specific examples.

Method	How it works
run()	Direct HTTP call, no queue
subscribe()	Queue-based, blocks until result
submit()	Queue-based, returns immediately (recommended)
stream()	Progressive output via SSE
realtime()	WebSocket, persistent connection

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Direct (run)

The simplest way to call a model. Sends a direct HTTP request to fal.run and returns the result. No queue, no retries, no polling.

import fal_client

result = fal_client.run("fal-ai/nano-banana-2", arguments={
    "prompt": "a sunset over mountains"
})
print(result["images"][0]["url"])

Use run for quick scripts, prototyping, or any model with fast response times where you want the lowest overhead. Because there is no queue involved, the call goes straight to a runner and returns the response directly. The tradeoff is that direct calls do not retry on failure. If the runner returns an error or times out, you get the error immediately.

For production use, prefer subscribe or submit so you get automatic retries and request durability through the queue.

Learn more

Direct and queue-backed synchronous calls

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Subscribe (Queue-backed synchronous)

Like run, but uses the queue under the hood. Submits a request, polls automatically, and blocks until the result is ready. You get automatic retries and reliability with a simple interface.

import fal_client

result = fal_client.subscribe("fal-ai/nano-banana-2", arguments={
    "prompt": "a sunset over mountains"
})
print(result["images"][0]["url"])

subscribe is a good choice when you want the simplicity of a blocking call combined with queue-backed reliability. It handles polling for you, so the code looks almost identical to run, but your request is durable and will be retried if a runner fails. Reach for it in simple integrations, backend scripts, or anywhere you do not need to manage the request lifecycle yourself.

Learn more

Direct and queue-backed synchronous calls

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Asynchronous (submit)

The recommended approach for production. Submit a request to the queue and return immediately, then poll for status or receive results via webhook.

Polling:

import time
import fal_client

handler = fal_client.submit("fal-ai/nano-banana-2", arguments={
    "prompt": "a sunset over mountains"
})

while True:
    status = handler.status(with_logs=True)

    if isinstance(status, fal_client.Queued):
        print(f"In queue, position: {status.position}")
    elif isinstance(status, fal_client.InProgress):
        for log in status.logs or []:
            print(log["message"])
    elif isinstance(status, fal_client.Completed):
        print(f"Done in {status.metrics.get('inference_time', '?')}s")
        break

    time.sleep(0.5)

result = handler.get()
print(result["images"][0]["url"])

Status types

The handler.status() method returns one of three types. Pass with_logs=True to include runner logs.

Type	Fields	Meaning
Queued	position (int)	Waiting in queue. position is how many requests are ahead.
InProgress	logs (list or None)	A runner is processing the request. logs contains messages if with_logs=True.
Completed	logs (list or None), metrics (dict)	Result is ready. metrics includes inference_time in seconds.

In JavaScript, the equivalent types are InQueueQueueStatus, InProgressQueueStatus, and CompletedQueueStatus. See the full Python SDK reference and JavaScript SDK reference for details.

Webhook (no polling needed):

import fal_client

handler = fal_client.submit("fal-ai/nano-banana-2",
    arguments={"prompt": "a sunset over mountains"},
    webhook_url="https://your-server.com/api/webhook"
)

Async inference is the recommended path for production because it works reliably at any scale. You can submit many requests in parallel and process them as they complete, use webhooks to build event-driven architectures without polling, and get full visibility into queue position and runner logs. The queue handles retries and request persistence automatically through the reliability layer.

Learn Async Inference

The recommended way to call models at scale

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Streaming (stream)

For models that produce output progressively. Each event arrives as it is generated, so you can display partial results without waiting for the full response. This is useful for showing image generation previews or streaming LLM tokens.

import fal_client

for event in fal_client.stream("fal-ai/flux-kontext-lora", arguments={
    "prompt": "a sunset over mountains"
}):
    print(event)

The stream() method connects to the /stream path on the model endpoint. Not all models support streaming. Check the model’s API documentation for availability.

Learn Streaming

Receive output as it’s generated

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Real-time (realtime)

For interactive applications that need the lowest possible latency. Opens a persistent WebSocket connection to a warm runner, enabling back-to-back requests without reconnection overhead. Only available for models with an explicit real-time endpoint.

import fal_client

with fal_client.realtime("fal-ai/fast-sdxl") as connection:
    connection.send({
        "prompt": "a sunset over mountains",
        "num_inference_steps": 2
    })
    result = connection.recv()
    print(result)

Learn Real-time

WebSocket connections for interactive apps

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Getting Started

Before calling any model, install and configure the fal client for your language. If you are building a browser-based app, you will also need a server-side proxy to keep your API key out of client-side code.

Client Setup

Install and configure the fal client

Proxy Setup

Keep your API key secure in client-side apps