Wan 3.0 duration -1 is Alibaba's smart length; Sume wants 2 to 30 s

Alibaba's Wan3.0 guide says a clip can run up to 30 seconds and that duration set to -1 means smart duration, where the model picks the length (read 2026-10-04). Smart length is convenient, but it makes the bill unpredictable.

Sume's wan-3.0 row takes whole seconds from 2 to 30. -1 is not a valid value, and the minimum is 2. Send an explicit duration, as the video generation docs show.

Cost of picking a length

The per-second rates are $0.0625, $0.125 and $0.25.

Choose a duration in code

For a vertical Short, pick the length you will keep, not the maximum. This helper rejects values Sume would.

def pick_duration(seconds: int) -> int:
    if seconds == -1:
        raise ValueError("-1 is Alibaba's smart duration; send a length")
    if not 2 <= seconds <= 30:
        raise ValueError("wan-3.0 takes whole seconds from 2 to 30")
    return seconds

for s in (5, 30):
    print(s, pick_duration(s))

If a shot needs more than 30 seconds, generate several clips and join them on Timeline.