FLUX 3 Image reference size: 256 px to 16 MP, and Sume URL rules

BFL's FLUX 3 Image takes 1 to 10 reference images, each between 256 x 256 px and 16 MP, as a URL or base64. Sume's FLUX ids today are FLUX.2 pro and flex, not FLUX 3, and the Sume Image API page states different reference rules: public HTTPS URLs only, and a per-model input_references count from the catalog. It publishes no pixel bounds for references, so a reference outside BFL's range is a case you test, not one the docs settle.

BFL's figures are from its FLUX 3 Image page, and Sume's from the Sume Image API page and errors page, all read 2026-10-02.

What are BFL's reference limits for FLUX 3 Image?

The parameter table says images is a string or list of 1 to 10 references, URL or base64, 256 x 256 px to 16 MP each. aspect_ratio defaults to auto, which follows the first reference and falls back to 1:1 when there is none. The result comes back as a polling_url, and result.sample has to be downloaded within 1 hour.

Does Sume serve FLUX 3 Image?

The OpenAPI model enum for POST /v1/images lists black-forest-labs/flux.2-pro and black-forest-labs/flux.2-flex as its FLUX ids; FLUX 3 is not in it. For FLUX 3 edits you would call BFL directly, with BFL's rules above.

What happens with a reference Sume cannot read?

Sume's docs say localhost, private-network and non-HTTPS URLs are rejected before submission. A public URL that Sume cannot fetch or mirror shows up as image_not_fetchable or input_media_unreachable, and the errors page says to check that the input is a public HTTPS image URL. The Sume docs show references only as public HTTPS image_url entries, so host the file instead of sending base64.

How do I stay safe on size?

Resize references to a size you have already seen succeed before you batch. Treat that as a habit, not a Sume rule: the Sume docs set no minimum or maximum.