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FLUX.1 Kontext [dev] Image to Image

fal-ai/flux-kontext/dev
Frontier image editing model.
Inference
Commercial use
Streaming
PlaygroundAPIExamples

About

FLUX.1 Kontext [dev] -- Frontier image editing model.

Kontext makes editing images easy! Specify what you want to change and Kontext will follow. It is capable of understanding the context of the image, making it easier to edit them without having to describe in details what you want to do.

Best Practices:

  • Be specific: Precise language gives better results. Use exact color names, detailed descriptions, and clear action verbs instead of vague terms.
  • Start simple: Begin with core changes before adding complexity. Test basic edits first, then build upon successful results. Kontext can handle very well iterative editing, use it.
  • Preserve intentionally: Explicitly state what should remain unchanged. Use phrases like "while maintaining the same [facial features/composition/lighting]" to protect important elements.
  • Iterate when needed: Complex transformations often require multiple steps. Break dramatic changes into sequential edits for better control.
  • Name subjects directly: Use "the woman with short black hair" or "the red car" instead of pronouns like "her", "it," or "this" for clearer results.
  • Use quotation marks for text: Quote the exact text you want to change: Replace 'joy' with 'BFL' works better than general text descriptions.
  • Control composition explicitly: When changing backgrounds or settings, specify "keep the exact camera angle, position, and framing" to prevent unwanted repositioning.
  • Choose verbs carefully: "Transform" might imply complete change, while "change the clothes" or "replace the background" gives you more control over what actually changes.

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

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-kontext/dev", {
  input: {
    prompt: "Change the setting to a day time, add a lot of people walking the sidewalk while maintaining the same style of the painting",
    image_url: "https://storage.googleapis.com/falserverless/example_inputs/kontext_example_input.webp"
  },
  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);

Streaming#

This model supports streaming requests. You can stream data directly to the model and get the result in real-time.

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

const stream = await fal.stream("fal-ai/flux-kontext/dev", {
  input: {
    prompt: "Change the setting to a day time, add a lot of people walking the sidewalk while maintaining the same style of the painting",
    image_url: "https://storage.googleapis.com/falserverless/example_inputs/kontext_example_input.webp"
  }
});

for await (const event of stream) {
  console.log(event);
}

const result = await stream.done();

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 case your app is running in an environment where you cannot set environment variables, you can set the API Key manually as a client configuration.
import { fal } from "@fal-ai/client";

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

3. Queue#

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-kontext/dev", {
  input: {
    prompt: "Change the setting to a day time, add a lot of people walking the sidewalk while maintaining the same style of the painting",
    image_url: "https://storage.googleapis.com/falserverless/example_inputs/kontext_example_input.webp"
  },
  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-kontext/dev", {
  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-kontext/dev", {
  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);

Read more about file handling in our file upload guide.

5. Schema#

Input#

prompt string* required

The prompt to edit the image.

image_url string* required

The URL of the image to edit.

num_inference_steps integer

The number of inference steps to perform. Default value: 28

seed integer

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

guidance_scale float

The CFG (Classifier Free Guidance) scale is a measure of how close you want the model to stick to your prompt when looking for a related image to show you. Default value: 2.5

sync_mode boolean

If set to true, the function will wait for the image to be generated and uploaded before returning the response. This will increase the latency of the function but it allows you to get the image directly in the response without going through the CDN.

num_images integer

The number of images to generate. Default value: 1

enable_safety_checker boolean

If set to true, the safety checker will be enabled. Default value: true

output_format OutputFormatEnum

Output format Default value: "jpeg"

Possible enum values: jpeg, png

acceleration AccelerationEnum

The speed of the generation. The higher the speed, the faster the generation. Default value: "none"

Possible enum values: none, regular, high

resolution_mode ResolutionModeEnum

Determines how the output resolution is set for image editing.

  • auto: The model selects an optimal resolution from a predefined set that best matches the input image's aspect ratio. This is the recommended setting for most use cases as it's what the model was trained on.
  • match_input: The model will attempt to use the same resolution as the input image. The resolution will be adjusted to be compatible with the model's requirements (e.g. dimensions must be multiples of 16 and within supported limits). Apart from these, a few aspect ratios are also supported. Default value: "match_input"

Possible enum values: auto, match_input, 1:1, 16:9, 21:9, 3:2, 2:3, 4:5, 5:4, 3:4, 4:3, 9:16, 9:21

{
  "prompt": "Change the setting to a day time, add a lot of people walking the sidewalk while maintaining the same style of the painting",
  "image_url": "https://storage.googleapis.com/falserverless/example_inputs/kontext_example_input.webp",
  "num_inference_steps": 28,
  "guidance_scale": 2.5,
  "num_images": 1,
  "enable_safety_checker": true,
  "output_format": "jpeg",
  "acceleration": "none",
  "resolution_mode": "match_input"
}

Output#

images list<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": [
    {
      "height": 768,
      "content_type": "image/jpeg",
      "url": "https://storage.googleapis.com/falserverless/example_outputs/kontext_example_output.jpeg",
      "width": 1024
    }
  ],
  "prompt": ""
}

Other types#

ImageSize#

width integer

The width of the generated image. Default value: 512

height integer

The height of the generated image. Default value: 512

Image#

url string* required
width integer* required
height integer* required
content_type string

Default value: "image/jpeg"

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