FLUX.1 [pro] Fill is a high-performance endpoint for the FLUX.1 [pro] model that enables rapid transformation of existing images, delivering high-quality style transfers and image modifications with the core FLUX capabilities.

fal-ai/flux-pro/v1/fill

Inference

Commercial use

Partner

Schema

LLMs

Playground API

fal-ai/flux-pro/v1/fill

Schema

fal-ai/flux-pro/v1/fill

Inference

Commercial use

Partner

Schema

LLMs

Playground API

1. Calling the API

2. Authentication

API Key

3. Queue

4. Files

5. Schema

About

FLUX.1 Fill [pro] API, next generation inpainting/outpainting model.

1. Calling the API#

Install the client#

The client provides a convenient way to interact with the model API.

npm install --save @fal-ai/client

Migrate to @fal-ai/client

The @fal-ai/serverless-client package has been deprecated in favor of @fal-ai/client. Install the new package and update your imports — see client setup.

Setup your API Key#

Set FAL_KEY as an environment variable in your runtime.

export FAL_KEY="YOUR_API_KEY"

Submit a request#

The client API handles the API submit protocol. It will handle the request status updates and return the result when the request is completed.

import { fal } from "@fal-ai/client";

const result = await fal.subscribe("fal-ai/flux-pro/v1/fill", {
  input: {
    prompt: "A knight in shining armour holding a greatshield with \"FAL\" on it",
    image_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
    mask_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
  },
  logs: true,
  onQueueUpdate: (update) => {
    if (update.status === "IN_PROGRESS") {
      update.logs.map((log) => log.message).forEach(console.log);
    }
  },
});
console.log(result.data);
console.log(result.requestId);

2. Authentication#

The API uses an API Key for authentication. It is recommended you set the FAL_KEY environment variable in your runtime when possible.

API Key#

In an environment where you cannot set environment variables, you can configure the API key manually on the client.

import { fal } from "@fal-ai/client";

fal.config({
  credentials: "YOUR_FAL_KEY"
});

Protect your API Key

When running code on the client-side (e.g. in a browser, mobile app or GUI applications), make sure to not expose your FAL_KEY. Instead, use a server-side proxy to make requests to the API. For more information, check out our server-side integration guide.

3. Queue#

Long-running requests

For long-running requests, such as training jobs or models with slower inference times, it is recommended to check the Queue status and rely on Webhooks instead of blocking while waiting for the result.

Submit a request#

The client API provides a convenient way to submit requests to the model.

import { fal } from "@fal-ai/client";

const { request_id } = await fal.queue.submit("fal-ai/flux-pro/v1/fill", {
  input: {
    prompt: "A knight in shining armour holding a greatshield with \"FAL\" on it",
    image_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
    mask_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
  },
  webhookUrl: "https://optional.webhook.url/for/results",
});

Fetch request status#

You can fetch the status of a request to check if it is completed or still in progress.

import { fal } from "@fal-ai/client";

const status = await fal.queue.status("fal-ai/flux-pro/v1/fill", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b",
  logs: true,
});

Get the result#

Once the request is completed, you can fetch the result. See the Output Schema for the expected result format.

import { fal } from "@fal-ai/client";

const result = await fal.queue.result("fal-ai/flux-pro/v1/fill", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b"
});
console.log(result.data);
console.log(result.requestId);

4. Files#

Some attributes in the API accept file URLs as input. Whenever that's the case you can pass your own URL or a Base64 data URI.

Data URI (base64)#

You can pass a Base64 data URI as a file input. The API will handle the file decoding for you. Keep in mind that for large files, this alternative although convenient can impact the request performance.

Hosted files (URL)#

You can also pass your own URLs as long as they are publicly accessible. Be aware that some hosts might block cross-site requests, rate-limit, or consider the request as a bot.

Uploading files#

We provide a convenient file storage that allows you to upload files and use them in your requests. You can upload files using the client API and use the returned URL in your requests.

import { fal } from "@fal-ai/client";

const file = new File(["Hello, World!"], "hello.txt", { type: "text/plain" });
const url = await fal.storage.upload(file);

Auto uploads

The client will auto-upload the file for you if you pass a binary object (e.g. File, Data).

Read more about file handling in our file upload guide.

5. Schema#

Input#

prompt string* required

The prompt to fill the masked part of the image.

seed integer

The same seed and the same prompt given to the same version of the model will output the same image every time.

sync_mode boolean

If True, the media will be returned as a data URI and the output data won't be available in the request history.

num_images integer

The number of images to generate. Default value: 1

output_format OutputFormatEnum

The format of the generated image. Default value: "jpeg"

Possible enum values: jpeg, png

safety_tolerance SafetyToleranceEnum

API only

The safety tolerance level for the generated image. 1 being the most strict and 5 being the most permissive. Default value: "2"

Possible enum values: 1, 2, 3, 4, 5, 6

Note: This property is only available through API calls.

enhance_prompt boolean

Whether to enhance the prompt for better results.

image_url string* required

The image URL to generate an image from. Needs to match the dimensions of the mask.

mask_url string* required

The mask URL to inpaint the image. Needs to match the dimensions of the input image.

{
  "prompt": "A knight in shining armour holding a greatshield with \"FAL\" on it",
  "num_images": 1,
  "output_format": "jpeg",
  "safety_tolerance": "2",
  "image_url": "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
  "mask_url": "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
}

Output#

images list<registry__image__fast_sdxl__models__Image>* required

The generated image files info.

timings Timings* required

seed integer* required

Seed of the generated Image. It will be the same value of the one passed in the input or the randomly generated that was used in case none was passed.

has_nsfw_concepts list<boolean>* required

Whether the generated images contain NSFW concepts.

prompt string* required

The prompt used for generating the image.

{
  "images": [
    {
      "url": "",
      "content_type": "image/jpeg"
    }
  ],
  "prompt": ""
}

Other types#

registryimagefast_sdxlmodelsImage#

url string* required

width integer* required

height integer* required

content_type string

Default value: "image/jpeg"

Related Models

1. Calling the API

2. Authentication

API Key

3. Queue

4. Files

5. Schema

About

FLUX.1 Fill [pro] API, next generation inpainting/outpainting model.

1. Calling the API#

Install the client#

The client provides a convenient way to interact with the model API.

npm install --save @fal-ai/client

Migrate to @fal-ai/client

The @fal-ai/serverless-client package has been deprecated in favor of @fal-ai/client. Install the new package and update your imports — see client setup.

Setup your API Key#

Set FAL_KEY as an environment variable in your runtime.

export FAL_KEY="YOUR_API_KEY"

Submit a request#

The client API handles the API submit protocol. It will handle the request status updates and return the result when the request is completed.

import { fal } from "@fal-ai/client";

const result = await fal.subscribe("fal-ai/flux-pro/v1/fill", {
  input: {
    prompt: "A knight in shining armour holding a greatshield with \"FAL\" on it",
    image_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
    mask_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
  },
  logs: true,
  onQueueUpdate: (update) => {
    if (update.status === "IN_PROGRESS") {
      update.logs.map((log) => log.message).forEach(console.log);
    }
  },
});
console.log(result.data);
console.log(result.requestId);

2. Authentication#

The API uses an API Key for authentication. It is recommended you set the FAL_KEY environment variable in your runtime when possible.

API Key#

In an environment where you cannot set environment variables, you can configure the API key manually on the client.

import { fal } from "@fal-ai/client";

fal.config({
  credentials: "YOUR_FAL_KEY"
});

Protect your API Key

3. Queue#

Long-running requests

Submit a request#

The client API provides a convenient way to submit requests to the model.

import { fal } from "@fal-ai/client";

const { request_id } = await fal.queue.submit("fal-ai/flux-pro/v1/fill", {
  input: {
    prompt: "A knight in shining armour holding a greatshield with \"FAL\" on it",
    image_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
    mask_url: "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
  },
  webhookUrl: "https://optional.webhook.url/for/results",
});

Fetch request status#

You can fetch the status of a request to check if it is completed or still in progress.

import { fal } from "@fal-ai/client";

const status = await fal.queue.status("fal-ai/flux-pro/v1/fill", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b",
  logs: true,
});

Get the result#

Once the request is completed, you can fetch the result. See the Output Schema for the expected result format.

import { fal } from "@fal-ai/client";

const result = await fal.queue.result("fal-ai/flux-pro/v1/fill", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b"
});
console.log(result.data);
console.log(result.requestId);

4. Files#

Some attributes in the API accept file URLs as input. Whenever that's the case you can pass your own URL or a Base64 data URI.

Data URI (base64)#

Hosted files (URL)#

You can also pass your own URLs as long as they are publicly accessible. Be aware that some hosts might block cross-site requests, rate-limit, or consider the request as a bot.

Uploading files#

We provide a convenient file storage that allows you to upload files and use them in your requests. You can upload files using the client API and use the returned URL in your requests.

import { fal } from "@fal-ai/client";

const file = new File(["Hello, World!"], "hello.txt", { type: "text/plain" });
const url = await fal.storage.upload(file);

Auto uploads

The client will auto-upload the file for you if you pass a binary object (e.g. File, Data).

Read more about file handling in our file upload guide.

5. Schema#

Input#

prompt string* required

The prompt to fill the masked part of the image.

seed integer

The same seed and the same prompt given to the same version of the model will output the same image every time.

sync_mode boolean

If True, the media will be returned as a data URI and the output data won't be available in the request history.

num_images integer

The number of images to generate. Default value: 1

output_format OutputFormatEnum

The format of the generated image. Default value: "jpeg"

Possible enum values: jpeg, png

safety_tolerance SafetyToleranceEnum

API only

The safety tolerance level for the generated image. 1 being the most strict and 5 being the most permissive. Default value: "2"

Possible enum values: 1, 2, 3, 4, 5, 6

Note: This property is only available through API calls.

enhance_prompt boolean

Whether to enhance the prompt for better results.

image_url string* required

The image URL to generate an image from. Needs to match the dimensions of the mask.

mask_url string* required

The mask URL to inpaint the image. Needs to match the dimensions of the input image.

{
  "prompt": "A knight in shining armour holding a greatshield with \"FAL\" on it",
  "num_images": 1,
  "output_format": "jpeg",
  "safety_tolerance": "2",
  "image_url": "https://storage.googleapis.com/falserverless/flux-lora/example-images/knight.jpeg",
  "mask_url": "https://storage.googleapis.com/falserverless/flux-lora/example-images/mask_knight.jpeg"
}

Output#

images list<registry__image__fast_sdxl__models__Image>* required

The generated image files info.

timings Timings* required

seed integer* required

Seed of the generated Image. It will be the same value of the one passed in the input or the randomly generated that was used in case none was passed.

has_nsfw_concepts list<boolean>* required

Whether the generated images contain NSFW concepts.

prompt string* required

The prompt used for generating the image.

{
  "images": [
    {
      "url": "",
      "content_type": "image/jpeg"
    }
  ],
  "prompt": ""
}

Other types#

registryimagefast_sdxlmodelsImage#

url string* required

width integer* required

height integer* required

content_type string

Default value: "image/jpeg"

fal-ai/flux-pro/v1/fill

Table of contents

Table of contents

fal-ai/flux-pro/v1/fill

Table of contents

1. Calling the API

2. Authentication

3. Queue

4. Files

5. Schema

About

1. Calling the API#

Install the client#

Migrate to @fal-ai/client

Setup your API Key#

Submit a request#

2. Authentication#

API Key#

Protect your API Key

3. Queue#

Long-running requests

Submit a request#

Fetch request status#

Get the result#

4. Files#

Data URI (base64)#

Hosted files (URL)#

Uploading files#

Auto uploads

5. Schema#

Input#

Output#

Other types#

registry__image__fast_sdxl__models__Image#

Related Models

Table of contents

Table of contents

1. Calling the API

2. Authentication

3. Queue

4. Files

5. Schema

About

1. Calling the API#

Install the client#

Migrate to @fal-ai/client

Setup your API Key#

Submit a request#

2. Authentication#

API Key#

Protect your API Key

3. Queue#

Long-running requests

Submit a request#

Fetch request status#

Get the result#

4. Files#

Data URI (base64)#

Hosted files (URL)#

Uploading files#

Auto uploads

5. Schema#

Input#

Output#

Other types#

registry__image__fast_sdxl__models__Image#

Related Models

registryimagefast_sdxlmodelsImage#

registryimagefast_sdxlmodelsImage#