Black Forest LabsFastStandard

FLUX.2 Klein 4B

Very fast image generation and editing model. 4-step distilled, sub-second inference for production and near real-time applications.

2 credits

per image at 1MP (default); 2 credits at 0.25-0.5MP, 4 at 2MP, 8 at 4MP

4-step distilled model — sub-second inference

Supports both text-to-image and image-to-image editing (up to 5 reference images)

Selectable output resolution from 0.25MP to 4MP

Optional go_fast mode for additional speed

Billed by output megapixels, so smaller previews cost less

Run it right now

Test this model instantly in the Console Playground — no code required

Use with AI Assistant

Copy usage instructions for Claude, ChatGPT, or other AI

llms.txtllms.txt ↗

Quick Start

curl -X POST "https://api.core.today/v1/predictions" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: cdt_your_api_key" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-4b",
  "input": {
    "prompt": "A surreal underwater or cosmic garden scene with bioluminescent flora against a deep navy background",
    "output_megapixels": "1",
    "aspect_ratio": "1:1"
  }
}'

Parameters

Parameter	Type	Required	Default	Description
`prompt`	string	Yes	-	Text prompt for image generation
`images`	array	No	[]	Input images for image-to-image generation (max 5)
`aspect_ratio`	string	No	1:1	Aspect ratio for the generated image. Use match_input_image to match the first input image 1:116:99:163:22:34:33:45:44:521:99:21match_input_image
`output_megapixels`	string	No	1	Resolution of the output image in megapixels. Higher values cost more credits 0.250.5124
`seed`	integer	No	-	Random seed. Set for reproducible generation
`go_fast`	boolean	No	false	Run faster predictions with additional optimizations
`output_format`	string	No	jpg	Format of the output images webpjpgpng
`output_quality`	integer	No	95	Quality when saving the output images, from 0 to 100. 100 is best quality, 0 is lowest quality. Not relevant for .png outputs.
`disable_safety_checker`	boolean	No	false	Disable safety checker for generated images.

How to Provide File Input

There are 3 ways to provide files for the images parameter:

Recommended

Direct Upload (Multipart)

Attach files directly to POST /v1/predictions/upload. No separate upload step needed.

curl -X POST "https://api.core.today/v1/predictions/upload" \
  -H "X-API-Key: cdt_your_api_key" \
  -F "model=black-forest-labs/flux-2-klein-4b" \
  -F 'input={"prompt":"your prompt here"}' \
  -F "file:images=@your_file.png"

Image URL

Pass a publicly accessible URL directly. You can also use file_url from the Storage API.

{
  "model": "black-forest-labs/flux-2-klein-4b",
  "input": {
    "prompt": "your prompt here",
    "images": ["https://example.com/image.jpg"]
  }
}

See the File Upload docs for more upload methods including Presigned URLs.

Common Parameters

Common parameters used when calling POST /v1/predictions.

Parameter	Type	Required	Default	Description
`model`	string	Yes	-	Model identifier
`input`	object	Yes	-	Object containing the model-specific parameters from the table above
`output_folder`	string	No	-	Folder path for output files (max 256 chars, '..' not allowed)
`webhook_url`	string	No	-	Webhook URL to call on completion
`is_public`	boolean	No	false	If true, output files are also available via permanent public URLs

Examples

Fast 1MP Generation (Default)

Default 1-megapixel text-to-image generation

curl -X POST "https://api.core.today/v1/predictions" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: cdt_your_api_key" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-4b",
  "input": {
    "prompt": "A surreal underwater or cosmic garden scene with bioluminescent flora against a deep navy background",
    "output_megapixels": "1",
    "aspect_ratio": "1:1"
  }
}'

Low-Cost Preview

0.25-megapixel draft for quick prompt iteration

curl -X POST "https://api.core.today/v1/predictions" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: cdt_your_api_key" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-4b",
  "input": {
    "prompt": "A neon-lit cyberpunk alley at night, concept sketch",
    "output_megapixels": "0.25"
  }
}'