Seedance 2.5 references only, no prompt: Sume still needs a prompt

Sume does not accept a references-only video request. In the request parameter table, prompt is a required string, so send at least a short prompt even when you attach image, video or audio references. Runway's Seedance 2.5 differs: its changelog says you may omit promptText when at least one reference is provided.

Sources: the Runway Dev changelog and Sume's video generation docs, read 2026-10-01.

What does Runway allow?

The August 7, 2026 entry says Seedance 2.5 text-to-video can run from references alone: omit promptText when at least one image, video or audio reference is provided. It lists reference limits of up to 30 images, 10 videos and 10 audio clips.

What does Sume require?

The parameter table marks model and prompt as required. Audio and video references are honored by the Seedance 2.x models, Wan 3.0, MiniMax H3 and MiniMax H3 Max, and seedance-2.5 accepts 4–30 seconds at 480p, 720p and 1080p.

What prompt should I send with references?

Describe what the references should do, not what they look like. For tagging references inside a prompt, see Seedance 2.5 omni reference with @ tags. A one-line prompt that names the motion and camera is enough to satisfy the field.

What should I do if my pipeline sends empty prompts?

Add a default string at the boundary before calling Sume, and validate it is non-empty. Do not rely on the provider-side behavior, because the Sume field is the contract your client meets.