FLUX.2-klein-4B

Summary: FLUX.2-klein-4B is a compact, efficient text-to-image model developed by Black Forest Labs, designed to deliver high-quality image generation with a reduced 4B parameter footprint. Building on the FLUX architecture, the klein variant prioritises speed and resource efficiency while maintaining strong visual fidelity, making it well-suited for content creation, rapid prototyping, and applications where low-latency generation is essential.

Image quality	Speed	Input	Output
Medium	High	Text	Image

Central parameters

Description: Compact 4B-parameter image generation model optimised for fast, high-quality visual output with low resource overhead.

Model identifier: black-forest-labs/FLUX.2-klein-4B

IONOS CLOUD AI Model Hub lifecycle and alternatives

IONOS CLOUD start date	End of Life	Alternative	Successor
June 16, 2026	N/A	N/A

Origin

Provider	Country	License	Flavor	Release
Black Forest Labs	Germany	License	Base	TBD

Technology

Input Length	Iterations	Quantization	Multilingual	Further details
256	4	8bit	Yes	Hugging Face

Modalities

Text	Image	Audio
Input	Output	Not supported

Endpoints

Chat Completions	Embeddings	Image generation	Image editing
Not supported	Not supported	v1/images/generations	v1/images/edits

Features

Streaming	Reasoning	Tool calling	Image editing
Not supported	Not supported	Not supported	Supported

Usage example

Parameter	Values
n	1–10
output_format	jpg, jpeg, png, webp
size	"widthxheight" format — both dimensions must be multiples of 16 and between 64–2048. Default: "1024x1024". Example values: "1024x1024", "1536x1024", "1024x1536", "2048x2048", "2048x1152"

Generate an Image

The following example demonstrates how to generate an image using FLUX.2-klein-4B.

API Endpoint: POST https://openai.inference.de-txl.ionos.com/v1/images/generations

Request:

{
  "model": "black-forest-labs/FLUX.2-klein-4B",
  "prompt": "A futuristic city with flying cars at sunset",
  "n": 1,
  "size": "1024x1024",
  "output_format": "jpeg"
}

Response:

{
  "created": 1589478378,
  "data": [
    {
      "b64_json": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII="
    }
  ]
}

Edit an image

The following example demonstrates how to edit an image using FLUX.2-klein-4B.

API Endpoint: POST https://openai.inference.de-txl.ionos.com/v1/images/edits

Request format: multipart/form-data

Request:

{
  "model": "black-forest-labs/FLUX.2-klein-4B",
  "prompt": "Add a rainbow in the sky above the cityscape",
  "url": "https://example.com/cityscape.png",
  "n": 1,
  "size": "1024x1024",
  "response_format": "b64_json"
}

Response:

{
  "created": 1589478378,
  "data": [
    {
      "b64_json": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII="
    }
  ]
}

Rate limits

Rate limits ensure fair usage and reliable access to the AI Model Hub. In addition to the contract-wide rate limits, the following rate limits apply:

Endpoint or Scope	Limit	Notes
Image generation	10 images/minute (base)	Additional limit specifically for images
	20 images/minute (burst)	Short bursts allowed; after a burst, burst quota refills at the base rate (10 images/minute)