Imagen 4 Ultra API on Sume: 1K and 2K, and the Fast id

On Sume's image API, google/imagen-4-ultra takes a resolution of 1K or 2K, and 2K is used when you leave it out. google/imagen-4-fast is a separate id with no resolution setting. Both accept a text prompt only, both list the same five aspect ratios, and the price is one flat rate per image for each, whichever resolution you choose.

This is read from the Image API docs, the SDK hints and the catalog code, 2026-09-29. Whether Google itself still serves these models is covered in a separate post, linked below.

How do Imagen 4 Ultra and Fast differ in the request?

The only request-level difference in Sume's catalog is resolution. The SDK hint says it directly: "nano-banana and imagen-4-ultra use the K tiers". Sending resolution to the Fast id returns 400 unsupported_parameter.

Does 1K cost less than 2K?

No. The price table holds a single rate for imagen-4-ultra, $0.06 list, so the price line is $0.075 at both tiers, and one image reserves $0.08. Four images reserve $0.30. Pick 1K when a smaller file suits your page, not to save money. The Fast id is priced separately: $0.02 list, $0.025 on the line.

Can I edit a photo with Imagen 4?

Not through Sume. Both entries carry the constraint "text-to-image only; image_urls not accepted", and input_references is not honoured for them. For edits, choose a model whose endpoint record lists reference images, and see which image model to use.

How do I request each tier?

Send the catalog id and add resolution only for Ultra.

curl -X POST https://api.sume.com/v1/images \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "google/imagen-4-ultra",
    "prompt": "A glass teapot on a linen cloth, soft window light",
    "aspect_ratio": "4:3",
    "resolution": "1K"
  }'

When would I choose Fast over Ultra?

Sume's docs do not rank the two on image quality or speed, so that call is yours to test. What the catalog does show is the cost and the knobs: Fast is $0.025 per image with no resolution field, Ultra is $0.075 with a 1K or 2K choice. A practical loop is to draft prompts on Fast, where a batch of four reserves $0.10, then send the winning prompt once to Ultra. Because both share the same five aspect ratios, the composition you pick on one carries over to the other without re-cropping.

Remember that neither id accepts reference images. If your draft loop needs an input photo, this pair is the wrong tool.

Will these ids stay in the catalog?

Check GET /v1/images/models before you build on them. Sume's docs do not promise a date, and Google's own status is discussed in Imagen 4 API alternative on Sume. The price math for every model is in how Sume prices image API calls.