Imagen 4 Ultra $0.075 or Fast $0.025 on Sume: 40 hero images

The short answer

For 40 hero images, Imagen 4 Fast on Sume costs $1.00 (40 x $0.025) and Imagen 4 Ultra costs $3.00 (40 x $0.075). Ultra is three times the price. Both rows take only five aspect ratios (1:1, 16:9, 9:16, 4:3, 3:4), so neither can make a 4:5 or 21:9 image directly.

The two rows

Sume's catalog read on 2026-10-09 lists imagen-4-fast and imagen-4-ultra in the Image Router. The shared price list gives their per-image prices. The aspect list comes from the repo's image catalog, which says Imagen 4 uses aspect_ratio only, with no 4:5 and no custom pixels.

A cheap way to choose

Draft with Fast, keep the best prompts, and render only those again on Ultra. If you draft 40 prompts on Fast ($1.00) and re-render 8 on Ultra (8 x 0.075 = $0.60), the run costs $1.60 instead of the $3.00 for 40 Ultra images, a saving of $1.40. The saving shrinks as the share you re-render grows: at 20 of 40 it is $1.00 + $1.50 = $2.50.

Quality is a judgment you make from your own prompts. This post does not compare output quality, only price and the parameters Sume lists.

What to put in the prompt

Hero images fail most often on composition, not on detail. State the subject, the camera position, the light, and where empty space should sit for headline text. For a 16:9 hero, ask for the subject on the left third so a headline fits on the right. Use the same sentence on Fast and Ultra, so any difference you see comes from the model and not the prompt.

Save each prompt with the model, the ratio and the usage.cost from the response. After 40 images you will have a small table of cost per kept image, which is the number that matters.

Reading the 40-image result

After the run, sort the 40 pairs by your own score, not by price. The useful figure is the share of images you would ship. If Fast ships 12 of 40 and Ultra ships 24 of 40, the cost per kept image is $1.00 / 12 = $0.083 for Fast and $3.00 / 24 = $0.125 for Ultra. The example numbers are placeholders for your own counts, but the formula is the point.

A cheap model that needs three tries can cost more than an expensive one that needs one, so the keep rate is as important as the list price.

A 16:9 or 9:16 hero is covered. For Instagram 4:5, generate 3:4 and crop to 1080 x 1350 in your own code, or pick a model that lists 4:5, such as Nano Banana 2.1 or a Seedream row. For a 21:9 banner, use Nano Banana 2.1 or a FLUX.2 row. A request that sets a ratio a model does not list is rejected with 400 unsupported_parameter; Sume does not quietly substitute another ratio.