Nano Banana Pro 21:9: Gemini's ratio list vs Sume's catalog

21:9 works on Sume with google/nano-banana-pro and google/nano-banana-2, which both list it in their aspect-ratio catalogs. It is not on the GPT Image 2.5 list (auto, 1:1, 16:9, 9:16, 4:3, 3:4, 5:4, 9:8, 4:5). A model only accepts values its descriptor lists, so read the catalog before you pin one.

Gemini's list is from Google's image generation page; Sume's from the Image API docs and the contract code. Both read 2026-10-01.

Which ratios does Gemini list?

Google's page lists 1:1, 3:2, 2:3, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9 and 21:9. Sizes vary by model: 3.1 Flash supports 512, 1K, 2K and 4K, and 3 Pro supports 1K, 2K and 4K.

What does Sume list?

How do I request it?

Send aspect_ratio alongside a resolution tier.

curl -X POST https://api.sume.com/v1/images \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "google/nano-banana-pro",
    "prompt": "Cinematic ultrawide of a desert highway at dusk",
    "aspect_ratio": "21:9",
    "resolution": "2K"
  }'

What if my model rejects it?

You get 400 unsupported_parameter. Call GET /v1/images/models and read that model's supported_parameters, or switch to a model whose descriptor lists 21:9.