Flux 2 Flex vs Flux 2 Pro on Sume: $0.0625 vs $0.0375 per image

On Sume, Flux 2 Pro and Flux 2 Flex differ in price and nothing else that the catalog publishes. Pro bills $0.0375 per image and Flex $0.0625, which is 1.67 times more for Flex. Both list 13 aspect ratios, take reference images, return png, jpeg or webp, and cap n at 4.

What the catalog says

Reading the table

Because the descriptors match, you cannot choose between them from the API shape. The choice is about the image you get for your own prompts. Sume's docs do not rank them, so this post does not either; it gives you the cost of finding out.

A 30-prompt A/B at one image per prompt costs 30 x $0.0375 = $1.125 on Pro and 30 x $0.0625 = $1.875 on Flex. Running both costs $3.00 in total.

A fair test

• Use the same prompts, the same aspect_ratio and n: 1 on both ids, so that price is the only variable you did not choose.
• Include at least one edit case with an input_references photo, since both ids accept references.
• Judge at delivery size. A 16:9 thumbnail is read at a few hundred pixels, so zoomed-in flaws matter less than composition.
• Log usage.cost from each response so that the billed amount, not an estimate, enters your sheet.

When the dearer one pays off

If Flex saves a retry, it is cheaper. With a $0.0375 Pro price and $0.0625 Flex price, one extra Pro retry per good image (two calls, $0.075) already costs more than one Flex call. If Pro lands a usable image on the first try for most prompts, stay on Pro. That is a measurement for your prompts, not a property of the models.

For ultra-wide work, both list 21:9 and 9:21, so a cinematic title card or a tall story strip does not need a different model.

Cost of a routing rule

A common setup is Pro by default and Flex for the prompts that fail review. If one in five prompts needs a Flex re-run, a batch of 100 prompts costs 100 x $0.0375 + 20 x $0.0625 = $5.00 billed. A batch run entirely on Flex costs $6.25, and one entirely on Pro costs $3.75. Your own rate of failures sets the real number, so count them for a week before you pick a rule.

Keep both ids behind a single setting in your code, and store the id that made each image next to the file. When a client asks why one image looks different from another, the answer is in that record, and a re-run on the same id is a one-line change.

Pin the id

Pin the full org/slug id and read the price from GET /v1/images/models/{id}/endpoints before large batches. The pricing line there is the amount charged to your wallet, margin included. See the Image API page for the request fields.