BFL modelsimage generation api

bfl/flux-1/fill

Name: Flux 1 Fill
Author: BFL

Flux 1 Fill is BFL's intelligent image editing model. Transform, retouch, and reimagine existing images using text prompts - from background replacement to artistic style conversion.

Input

Prompt(string)

The prompt to fill the masked part of the image.

Image URL or upload(string)

Upload

PNG, JPEG, WebP, or GIF · 20 MiB maximum

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

This field is required.

Image URL or upload(string)

Upload

PNG, JPEG, WebP, or GIF · 20 MiB maximum

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

Output Format(string)

The format of the generated image. Allowed values: jpeg, png.

Seed(integer)

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

Idle

Example output — click Run to generate your own

Production endpoint

Send your first request

OpenAI-compatible endpoint with unified authentication and usage tracking.

POSThttps://api.sandbase.ai/v1/run

Model IDbfl/flux-1/fill

Input Schema

5 parameters · 2 required · 3 optional

Parameter	Type	Required	Description
`image`	string	Required	The image URL to generate an image from. Needs to match the dimensions of the mask.
`prompt`	string	Required	The prompt to fill the masked part of the image.
`mask`	string	Optional	The mask URL to inpaint the image. Needs to match the dimensions of the input image.
`seed`	integer	Optional	The same seed and the same prompt given to the same version of the model will output the same image every time.
`output_format`	string	Optional	The format of the generated image. · Options: jpeg, png · Default: "jpeg" jpegpng

Output Schema

Field	Type	Description
`id`	string	Unique identifier for the generation task
`status`	string	Task status: pending, running, completed, failed, timeout
`model`	string	Model used for the generation
`outputs`	array	Array of output items
`outputs[].url`	string	URL of the generated artifact
`outputs[].content_type`	string	MIME type (e.g. image/png, video/mp4)
`error`	object \| null	Error details if failed, null on success
`error.type`	string	Machine-readable error type code
`error.message`	string	Human-readable error description

Async Workflow

This model uses asynchronous execution. Submit a request and poll for the result.

Submit — POST to /v1/run, receive an id
Poll — GET /v1/run/{id} until status is completed, failed, or timeout
Retrieve — Read outputs from the completed response

Code Examples

Ready-to-run snippets

# Step 1: Submit
curl -X POST https://api.sandbase.ai/v1/run \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
  "model": "bfl/flux-1/fill",
  "mask": "https://static.sandbase.ai/examples/bfl/flux-1/fill/input_mask_1.jpeg",
  "image": "https://static.sandbase.ai/examples/bfl/flux-1/fill/input_image_0.jpeg",
  "prompt": "A knight in shining armour holding a greatshield with \"EROUTER\" on it",
  "output_format": "jpeg"
}'

# Step 2: Poll result (replace <id>)
curl https://api.sandbase.ai/v1/run/<id> \
  -H "Authorization: Bearer YOUR_API_KEY"

← Back to Flux 1 Fill

API README

Flux 1 Fill

Flux 1 Fill is Black Forest Labs’ targeted image reconstruction model for inpainting and outpainting. It generates content inside masked regions or beyond existing boundaries while reading surrounding context, allowing removals, replacements, repairs, and canvas extensions to blend with the source image.

Use precise masks and describe the final content rather than the editing operation alone. For inpainting, explain what belongs in the selected area and how it meets nearby texture and light; for outpainting, describe the environment, perspective, and composition that should continue beyond the original crop.

Highlights

Mask-aware inpainting. Reconstructs selected regions according to prompt and neighboring image context.
Contextual outpainting. Extends a scene beyond its current canvas with plausible new content.
Boundary-consistent synthesis. Matches perspective, texture, color, and illumination across edit edges.
Source-region preservation. Keeps unmasked content stable while concentrating generation where needed.

Pricing

Billing unit	Price
Per request	$0.05

When to Use

✅ Good fit	❌ Consider alternatives
The model's named workflow matches the source material and intended output	A different input modality or model route is required
A managed asynchronous result is suitable for the production pipeline	A synchronous, interactive editor is essential
The documented controls cover the required duration, framing, or format	The project needs controls outside this endpoint's schema
Creative iteration benefits from a repeatable request structure	Exact deterministic pixels, frames, geometry, or samples are mandatory
A finished downloadable media asset is the desired deliverable	Editable source layers or a native project file are required

Prompt Guide

For image-conditioned generation, state the intended result first, then add the subject or source treatment, progression, style, and delivery constraints. Keep one creative variable per phrase, use the documented field names for controls, and change one setting at a time when comparing results.

{
  "image": "https://example.com/start-frame.png",
  "output_format": "jpeg",
  "prompt": "A knight in shining armour holding a greatshield with \"EROUTER\" on it"
}

Technical Specs

Spec	Value
Model ID	`bfl/flux-1/fill`
Inputs	image, mask, output_format, prompt, seed
Required inputs	prompt, image
Output fields	content_type, url
Execution	Async (submit, then poll for result)
Output Format	jpeg / png

Related Models

bfl/flux-1/dev — Compare this concrete local family route.
bfl/flux-1/dev/edit — Compare this concrete local family route.
bfl/flux-1/dev/image-to-image — Compare this concrete local family route.