FLUX.2 flex steps and guidance: BFL has them, Sume does not

Only FLUX.2 [flex] has adjustable steps and guidance in BFL's lineup; the other tiers are listed as standard controls. Sume lists black-forest-labs/flux.2-flex but allows no provider passthrough in v1, so steps and guidance are not dials you can set there: a parameter the model does not list is rejected with 400 unsupported_parameter.

BFL facts are from its FLUX.2 overview; Sume facts from Image generation, read 2026-10-01.

What does BFL give flex?

The controls row of the overview table reads as follows.

What does Sume expose on flex?

The id is in the catalog. Parameters come from the model's supported_parameters, which you read from GET /v1/images/models. Sume's docs state allowed_passthrough_parameters is empty for every endpoint in v1, so provider.options must be omitted or empty. This post does not claim any specific list for flex beyond that; check the response.

What happens if I send steps anyway?

Expect 400 unsupported_parameter. The docs say unlisted parameters are rejected rather than silently dropped, which is useful: you find out immediately that your setting was not applied.

Where do I get control instead?

Through the prompt and the typed fields. See FLUX.2 flex text rendering for what flex is used for, and FLUX.2 API pricing for cost.