Veo 3.1 has no 1:1 square: 16:9 and 9:16 only, and where Sume does 1:1

Veo 3.1 cannot make a square or ultrawide clip. The Veo guide lists two aspect ratios: 16:9 (the default) and 9:16. On Sume, gemini-omni-flash-1.1 has the same two. If you need 1:1 or 21:9, pick another Sume model from the table below.

Aspect ratios by model

The Sume values come from the Video Router catalog, the same source that GET /v1/videos/models reads as supported_aspect_ratios. Read that field for the live list before you submit.

Models with no ratio field

grok-imagine-video-1.5, h3-max-recast and higgsfield-genjutsu list no aspect ratios, because they start from a source image or video. The Sume API validates against the catalog: a ratio a model does not advertise returns 400, and Sume does not silently drop it.

Read the live list

Run this against your own key to print the live list for every model. It uses the same GET /v1/videos/models route that the Sume docs describe, so you do not depend on this table staying current.

curl -s "https://api.sume.com/v1/videos/models" \
  -H "Authorization: Bearer $SUME_API_KEY" \
  | jq '.data[] | {id, supported_aspect_ratios}'

What to do for 1:1

Square is not in the Omni list, so a 1:1 feed ad cannot come from Omni directly. Two routes work: generate 16:9 or 9:16 and crop with a separate step, or pick a model that lists 1:1. Cropping a 16:9 clip to square keeps only the middle of the frame, so frame the subject in the center from the start.

For 1:1 on Sume, Kling 3 and Wan 3.0 list it, and the Seedance and MiniMax H3 models list it along with 21:9.