FLUX 3 Image Klein API

The FLUX 3 Image Klein API gives you access to the 5.6B-parameter open-weights model in Black Forest Labs' FLUX 3 Image family. On APIMart, use model flux-3-image-klein for text-to-image, editing or multi-reference work. Each request returns one image.

Klein is the smaller, faster and lower-cost model in the family. Through the API it also accepts seed, 1–16 steps and PNG or JPEG output. It does not support the grounding search option of FLUX 3 Image, and safety_tolerance uses the same 0–4 range.

image_urls accepts up to 10 HTTP(S) URLs or base64 images. The first image is the one being edited.

Choose a resolution tier — 768sq (768×768), 1k (~1 MP), 1.5k (~2 MP), 2k (~4 MP) or 4k (~16 MP) — with auto or one of 15 aspect ratios. width and height are not accepted at the moment; for a specific frame, combine aspect_ratio with resolution.

seed (0 to 4294967295) makes results reproducible with the same settings; leave it empty for a random seed. steps sets 1 to 16 denoising steps (default 16); fewer steps are faster and don't change the price. output_format returns jpeg (default) or png, and jpg is treated as jpeg.

Black Forest Labs publishes the Klein weights on Hugging Face under the license on its model card. According to Black Forest Labs, running the weights in a commercial product requires a commercial license from them. This page covers API access; for self-hosting terms, see Black Forest Labs' licensing page.

Each image is priced by its resolution tier only. Aspect ratio, the number of references, steps, seed and output_format don't change the price, and text-to-image costs the same as editing. See the pricing table on this page; the final charge is the completed task's cost.

Sign up for APIMart, add credits to your balance, then create an API key on the API Keys page of the dashboard. Send it as a Bearer token with each FLUX 3 Image Klein API request; the same key works for every model on APIMart.

POST /v1/images/generations returns a task_id. Query GET /v1/tasks/{task_id} until the task completes or fails, then save the image URL promptly and follow any expiry information returned.

Yes. Black Forest Labs' API reference calls it FLUX 3 Klein, and people also search for it as FLUX Klein, FLUX.3 Klein, FLUX3 Klein or BFL Klein. All of these names point to the same model, which you call on APIMart as flux-3-image-klein. Klein Base, the 50-step variant for fine-tuning, is released as open weights only and has no API.