FLUX 3 Image Klein: API, References and Editing Checks

• BFL release announcement

BFL reports internal quality and latency comparisons in the announcement. They are publisher evaluations, not measurements reproduced here. Choose your own acceptance criteria before using those charts to justify a production change: exact lettering, product geometry, background stability and time to an accepted file can matter more than a single overall score.

The model card distinguishes a base checkpoint for adaptation from a distilled checkpoint used by the API. It also explains that the image generator, text encoder, autoencoder and optional prompt-expansion model contribute to a local setup. A quantized weight file’s size is not the complete memory requirement.

• Official checkpoint card and local setup

Use the hosted route if your immediate question is whether an output fits the brief. Use local evaluation when deployment control or model adaptation is part of the requirement. Record checkpoint revision, inference implementation, precision and prompt-expansion settings when comparing local results. This guide does not install weights or benchmark a GPU.

The current BFL OpenAPI schema exposes POST /v1/flux-3-image-klein with x-key authentication. It requires prompt; the example explicitly chooses square 1k output and PNG. Running it submits a billable request to BFL. Set your own key privately on the server; no request was submitted for this article.

curl --fail-with-body 'https://api.bfl.ai/v1/flux-3-image-klein' \
  -H "x-key: $BFL_API_KEY" \
  -H 'Content-Type: application/json' \
  --data '{
    "prompt": "Editorial product photograph of an unbranded amber glass bottle on a pale limestone block. A single soft shadow falls right. Warm white background, front view, ample empty space above the bottle, no lettering.",
    "aspect_ratio": "1:1",
    "resolution": "1k",
    "output_format": "png",
    "seed": 19
  }'

The asynchronous response contains id and polling_url. Retain both and follow the returned polling URL according to BFL’s result contract. Do not resubmit merely because the image was not returned synchronously. A network interruption after submission requires checking the existing task before paying for another one.

• Official BFL OpenAPI request and response schemas

For references, the BFL field is images, accepting a string or list. The first reference is the edit source and supplies the default size. Explicit width and height override resolution and aspect_ratio. These names differ from SJolt image-edit fields, so copy a complete provider contract rather than mixing parameters from tutorials.

The card advises full scene captions or prompt upsampling. Its reference CLI performs expansion by default, while the documented Diffusers pipeline needs that step supplied separately. References anchor content but do not guarantee unchanged structure. The card also warns that bounding boxes guide placement rather than acting as hard pixel masks.

• Model card: prompting and limitations
• BFL bounding-box format and examples

For a bottle-background change, make the first reference the original product frame. Add a second reference only if it conveys a clear requirement such as surface texture. Describe the whole intended shot and name the specific change. Keep your source and requested edit together so the reviewer knows what must remain stable.

If exact background preservation is essential, verify a documented preservation workflow and compare decoded pixels in the intended region. Do not infer a hard-mask guarantee from the word “box.” Keep final legal copy and editable typography in a layout tool when exact characters are required. A visually attractive candidate can still fail the production brief.

The FLUX Kommunity License is not an unrestricted MIT or Apache grant. It permits non-commercial uses and provides a commercial-output exception for Qualifying Users, defined by combined gross annualized revenue below US$5 million. That exception has conditions, including output review or filtering and applicable AI disclosures. Other commercial uses require checking BFL’s licensing terms.

• FLUX Kommunity License, including definitions and conditions

Before choosing self-hosting, identify who will operate the model, how outputs will be distributed and whether your use fits the actual grant. Keep the license revision with the selected checkpoint. Do not reuse an older FLUX family member’s license assumption or assume that downloading a file grants every intended commercial right.

For an image workflow already built on SJolt, FLUX.2 Pro is a separately supported option. Its text-to-image and image-edit operations have distinct routes; the latter accepts one to six image_urls. FLUX 3 on SJolt is video generation. Neither route is an alias for the BFL Image Klein endpoint described above.

• SJolt FLUX.2 Pro image routes
• SJolt FLUX 3 video routes
• Current model catalog

Compare alternatives using one approved brief and a fixed review checklist, then record the exact model and settings for each candidate. Retain the chosen asset in your project and use a new request only for an intentional revision. This guide verifies source and contract details; it claims no generation result, quality winner or live integration of Image Klein.