21:9 ultrawide AI video API: which Sume models accept it

Seedance 2.5, Seedance 2, 2 Fast and 2 Mini, MiniMax H3 and MiniMax H3 Max list 21:9 in their supported aspect ratios on Sume. Wan 3.0 (16:9, 4:3, 1:1, 3:4, 9:16), Kling 3 (16:9, 9:16, 1:1) and Gemini Omni Flash 1.1 (16:9, 9:16) do not. Pass aspect_ratio as 21:9 only to a model that lists it.

Aspect ratios by model (read 2026-10-04)

Source: the Sume video catalog.

A 21:9 request

This asks for a cinematic wide frame from Seedance 2.5 at 1080p.

curl -X POST "https://api.sume.com/v1/videos" \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "seedance-2.5",
    "prompt": "A train crosses a canyon bridge, anamorphic look",
    "duration": 8,
    "resolution": "1080p",
    "aspect_ratio": "21:9"
  }'

What if you need 21:9 from a model without it

Render at the widest supported ratio, 16:9, and crop to 21:9 afterwards with the video filter. That throws away part of the frame, so frame your prompt with the crop in mind.

Lengths and resolutions for the 21:9 models

Seedance 2.5 runs 4 to 30 seconds and Seedance 2 and its variants 4 to 15, all at 480p, 720p and 1080p. MiniMax H3 runs 5 to 15 seconds at native 480p and 768p, and H3 Max adds 1080p. Pick on length first.