AIREITER
FLUX 3 Klein AI Image Generator and API
FLUX 3 Klein is a compact, 5.6B-parameter version of FLUX 3 Image from Black Forest Labs. It is built for image editing and runs fast, while keeping the precise edits and text rendering of the full FLUX 3 Image model.
Edit with an instruction
Upload an image and say what to change. Klein keeps the rest of the picture as it was.
Text to image
Generate photography, illustration, and typography from a prompt alone.
Up to 3 references
Combine a subject, a product, and a style from up to three images in one result.
1 to 4 images at 1K or 2K
Get one, two, or four images per run, at 1K (default) or 2K.
What to Create with FLUX 3 Klein
Quick photo edits
Change the season, lighting, color, or background of a photo with one sentence.
Product and style mashups
Put a product from one image into the scene or style of another.
Posters and typography
Generate layouts with legible headlines, labels, and signs.
Fast drafts at volume
Generate four variations at once to compare ideas before you pick one.
Supported FLUX 3 Klein Controls
The playground and the API expose the same five parameters.
Prompt
Required. Up to 4,000 characters. Describe the image, or write the edit you want. Klein expands short prompts automatically before generating.
Reference images
Optional, up to 3. JPEG, PNG, or WEBP, up to 10MB each. The first image is the one being edited.
Aspect ratio
1:1 (default), 5:4, 4:5, 4:3, 3:4, 16:9, or 9:16.
Resolution
1K (default) or 2K.
Output number
1 (default), 2, or 4 images per run.
How to Use FLUX 3 Klein
Four steps, in the browser or through the API.
Add reference images
Skip this for text to image. To edit, upload the image to change first, then up to two more for subject or style.
Write the prompt
Describe the scene, or write the edit as an instruction, such as "make it a winter night".
Pick size and count
Choose the aspect ratio (1:1 by default), 1K or 2K, and how many images to generate.
Generate
Review the results and download the one you want, or refine the prompt and run it again.
Use FLUX 3 Klein through the AIReiter API
Submit one task and query the same external task ID until it reaches a terminal state.
Model ID
Send flux_3_klein as the model value in the request body.
Submit a task
POST /api/openapi/submit with the model, a unique out_task_id, and params: prompt, image_url, aspect_ratio, resolution, and output_n.
Query the result
POST /api/openapi/query with the same out_task_id until the status is completed or failed. Completed responses include the image URLs.
Input rules
prompt is required, up to 4,000 characters. image_url takes up to 3 URLs. aspect_ratio is 1:1, 5:4, 4:5, 4:3, 3:4, 16:9, or 9:16. resolution is 1K or 2K, output_n is 1, 2, or 4.
Related AI Image Models on AIReiter
FLUX 3 Klein FAQ
Answers about editing, references, sizes, and API usage.
/ 01What is FLUX 3 Klein?
FLUX 3 Klein is a compact, open-weights version of FLUX 3 Image from Black Forest Labs, released in October 2026. It has 5.6B parameters and is built for fast image editing and text-to-image generation.
/ 02How is FLUX 3 Klein different from FLUX 3 Image?
Klein is much smaller, so it runs faster and costs less per image. It keeps the precise editing of FLUX 3 Image and is the better fit for quick edits and high-volume drafts.
/ 03Can FLUX 3 Klein edit my photos?
Yes. Upload the photo as the first reference image and write the change as an instruction. Klein keeps the parts you don't mention.
/ 04How many reference images can I use?
Up to 3 on AIReiter. The first is the image being edited; the others can supply a subject, a product, or a style.
/ 05What sizes does FLUX 3 Klein support?
1K or 2K, in 1:1, 5:4, 4:5, 4:3, 3:4, 16:9, or 9:16.
/ 06How many images can I get per run?
1, 2, or 4. Each image is billed separately.
/ 07How long can the prompt be?
Up to 4,000 characters. Short prompts work too: Klein expands them into a full scene description before generating.
/ 08Which API model ID should I use?
Use flux_3_klein with POST /api/openapi/submit, then poll POST /api/openapi/query with the same out_task_id.