Wan 3.0 seed and size: why the API returns 400 unsupported_parameter
wan-3.0 on Sume rejects seed and size rather than ignoring them. Use resolution and aspect_ratio instead. Why the 400 happens and how to fix the request.
If a wan-3.0 request returns 400 unsupported_parameter, you sent a field no v1 model accepts, most often size or seed, or a non-empty provider.options. Sume rejects these loudly instead of dropping them, so you are never billed for a clip that ignored what you asked. Use resolution and aspect_ratio in place of size, and drop seed.
This follows the Video generation docs, read 2026-09-29, which list these differences from the OpenRouter video API that the route follows.
Which fields cause it?
| Field | Why it is rejected | What to send |
|---|---|---|
size | Every v1 model reports supported_sizes: null | resolution plus aspect_ratio |
seed | No v1 model accepts it; each reports seed: false | Nothing; leave it out |
provider.options | v1 runs one backend per model; the passthrough list is empty | Nothing; leave it out |
How do I get 1280x720?
Send resolution: "720p" and aspect_ratio: "16:9". Wan 3.0 accepts 480p, 720p and 1080p, and the ratios 16:9, 4:3, 1:1, 3:4 and 9:16.
Can I get the same clip twice without a seed?
No, and do not expect it. To avoid paying twice for one intended clip, send an Idempotency-Key on submit: a replay returns the original job. To reuse a clip you like, keep the file it returned.
How do I see what a model accepts?
Call GET /v1/videos/models and read the entry for wan-3.0: supported_resolutions, supported_aspect_ratios, supported_durations, supported_frame_images, supported_input_references, seed and allowed_passthrough_parameters.
Sources
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