Black Forest Labs’ release notes describe FLUX 3 Image as one endpoint for generation and editing, with bounding boxes placed in the prompt and up to ten references. This guide turns those features into prompt habits. The templates are our own; results vary, so test them.
What the release notes say
- Custom sizes (October 22): BFL says the endpoint accepts
widthandheightup to 16.8MP. - Match the input (October 22):
resolution: "match_input"makes edits match the first reference image’s size, up to 4MP. - Better single-reference edits: BFL says edits follow instructions more closely, and prices are unchanged.
- Output and references: up to 4K output and up to ten references (see the launch summary). The open-weight Klein version supports the same features, per BFL.
Prompt habits for edits
- Say what must stay. Name the parts to keep before the change.
- Make one change at a time. Chain small edits instead of one long list.
- Use match_input for retouching so the result keeps the original framing.
Template: Keep the person, pose and lighting unchanged. Replace only the background with a quiet harbour at dusk. Do not add text.
Prompt habits for multiple references
Refer to each image by its job: Use the first image for the product shape, the second for the colour palette, the third for the lighting mood. Keep the number of references small until the result is stable.
Choosing a size
Pick the size for the destination first (banner, square post, poster), then write the prompt. Larger sizes cost more, so check BFL’s pricing before batch runs.
More basics: how to write better image prompts, the Flux tool page and Midjourney vs Flux.