Upload 30 reference images to a Sume Format run (images only)

A Sume Format run accepts up to 30 images as attachments[] on the create body, each with type: "input_image". That is the only attachment type today, so videos and audio files are not attachments, unlike Opus Clip's Motion Studio, which takes up to 10 videos and 10 audio files alongside its images. Video and audio references go by URL in input instead.

Limits are from the Formats docs, read 2026-10-01; the Opus Clip counts are from its Sept 18 changelog entry.

What does an attachment look like?

Each entry is an object with a type and exactly one image source. Fields as the docs list them:

How do I send a run with attachments?

Put them beside instruction and input, for example { "instruction": "Make a product hero from the attached photo.", "attachments": [{ "type": "input_image", "asset_id": "asset_..." }] }. filename is optional on an entry. Use asset_id for private images, since an image_url is fetched without credentials.

What if my references are videos or audio?

They are not attachable. Extract stills from a clip with video_inspect or the frames endpoint and attach those as images, or use a media step in the Format itself. For plain image generation with references see image generation API reference images.

Does the agent treat attachments as instructions?

The docs describe attachments as images the agent can look at. Put your requirements in instruction, which comes after the Format's own text, and keep the pictures as reference only.