FLUX.1 Fill [dev]

Name: FLUX.1 Fill [dev]
Brand: Black Forest Labs
SKU: flux-fill-dev
Price: 0.048 USD
Availability: InStock

Image generationAvailable

by Black Forest Labsflux-fill-dev

Black Forest Labs' open-weight inpainting and outpainting model, guidance-distilled from FLUX.1 Fill [pro]. You supply an image plus a mask and a prompt; it fills the masked region or extends the canvas with prompt-guided content that matches lighting and texture.

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Price: $0.048/image
Input → output: Text + Image → Image
Developer: Black Forest Labs
Updated: September 23, 2026

Playground

Try FLUX.1 Fill [dev]

Input & output

$0.048/image

Prompt

0 / 2,000

What to paint into the masked region

Mask

Mask marking the region to fill (white = edit)

Image

Source image to edit

Advanced settings (3)

Output format(optional)

Guidance(optional)0–100

Steps(optional)1–50

⌘/Ctrl + Enter

Output

Your image appears here.

This run

$0.048 · 4.8 credits

For accounts without a purchase: runs above 2 credits need a top-up.

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10 free credits ($0.10) when you sign up with Google

Usable 24 hours after sign-up, up to 5 runs per day and at most 2 credits per run. Other sign-in methods start without credits.

Examples

Real outputs from the public examples of this model on Replicate, with the prompt and settings that produced them. They were not generated live on this page.

Open full size
Input
Prompt
a spaceship
Open full size
Input
Prompt
a white paper cup
Open full size
Input
Prompt
a man in a blue jacket

About FLUX.1 Fill [dev]

TL;DRAs of September 23, 2026

FLUX.1 Fill [dev] is a model by Black Forest Labs in the Image generation category. On Railwail, FLUX.1 Fill [dev] costs $0.048 per image.

Pricing

Prices in US dollars. Usage is charged from prepaid credits.

Per image	$0.048 per image

1 credit = $0.01

Cost calculator

Price calculator

Results per run

/ run

Runs

Total

$4.80

480 credits

Per run

$0.048 · 4.8 credits

Fixed price per run, known before the run starts.

API

Call FLUX.1 Fill [dev] with your Railwail API key. Use this model ID in the request:

flux-fill-devAPI documentation Get an API key

No verified API example

The public API passes a different input format than this model needs. Use the playground above.

Specifications

Model ID: flux-fill-dev
Developer: Black Forest Labs
Category: Image generation
Input: Text, Image
Output: Image
Output formats: WEBP, JPG, PNG
Billing: Fixed price, known before the run
Catalog entry updated: September 23, 2026

Input parameters

Inputs and settings from the model's input schema. The example in the API section shows which of them the API accepts.

ParameterTypeDefaultAllowed values

maskrequired
Mask marking the region to fill (white = edit)
Type: Text
Default: –
Allowed values: –
imagerequired
Source image to edit
Type: Text
Default: –
Allowed values: –
promptrequired
What to paint into the masked region
Type: Text
Default: –
Allowed values: up to 2,000 characters
guidance
Type: Number
Default: 30
Allowed values: 0 to 100
output_format
Type: Choice
Default: webp
Allowed values: webp, jpg, or png
num_inference_steps
Type: Integer
Default: 28
Allowed values: 1 to 50

Use cases

Related guides

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All models in Image generation

Frequently asked questions

What is FLUX.1 Fill [dev]?

FLUX.1 Fill [dev] is a model by Black Forest Labs in the Image generation category.

How much does FLUX.1 Fill [dev] cost on Railwail?

On Railwail, FLUX.1 Fill [dev] costs $0.048 per image. The price is known before the run starts. Usage is paid from prepaid credits; 1 credit equals $0.01.

Which settings does FLUX.1 Fill [dev] support?

According to its input schema, FLUX.1 Fill [dev] knows these parameters: mask, image, prompt (up to 2,000 characters), guidance (0 to 100), output_format (webp, jpg, or png), and num_inference_steps (1 to 50).

How fast is FLUX.1 Fill [dev]?

There are not enough measured runs of FLUX.1 Fill [dev] on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is FLUX.1 Fill [dev] better than FLUX 1.1 Pro?

That depends on the task. FLUX.1 Fill [dev] (Black Forest Labs) and FLUX 1.1 Pro (Black Forest Labs) are both models in the Image generation category. The comparison page shows their prices and specifications side by side.

Compare FLUX.1 Fill [dev] and FLUX 1.1 Pro

Can FLUX.1 Fill [dev] use an image as input?

Yes. Send the image in the image parameter.

Comparable models

All in this category

FLUX 1.1 ProBlack Forest Labs
Black Forest Labs' flagship text-to-image model. Faster generation than FLUX.1 Pro at higher prompt adherence, with strong photorealism and reliable spatial composition. Runs as a hosted Replicate model.
$0.048/image
Same price per unit
Compare FLUX.1 Fill [dev] vs. FLUX 1.1 Pro
Flux 1.1 Pro UltraBlack Forest Labs
FLUX 1.1 Pro in ultra mode. Up to 4 megapixel images with raw mode for photorealism.
$0.072/image
50 % more expensive per unit
Compare FLUX.1 Fill [dev] vs. Flux 1.1 Pro Ultra
Flux DevBlack Forest Labs
Black Forest Labs' development model. Fast, high-quality image generation with LoRA support.
$0.0384/image
20 % cheaper per unit
Compare FLUX.1 Fill [dev] vs. Flux Dev

All models through one API

One API key for every model on Railwail. Usage is charged from prepaid credits, 1 credit = $0.01.

Get API key Browse all models