Last week we got Seedance 2.5 running on the official Ark channel, and since Chinese docs on this model are thin and English docs are thinner, here are the notes I wish someone had written before we started.

The quick facts first. One async endpoint, model id `doubao-seedance-2.5-face`. Each request produces 4 to 30 seconds of video at 480p or 720p, MP4 or MOV out. Audio is generated in the same pass: speech, sound effects, background music. Spoken lines go inside double quotes in the prompt, everything else reads as scene direction. References go up to 30 images + 10 videos + 10 audio tracks per request, a lone audio file is a valid input, and real-person reference material is allowed, which is what the "face" in the id means.

Now the parts that cost us time:

- Prompt is mandatory on every mode, including image-to-video. Minimum 3 characters. 2.0 let you throw a bare image; 2.5 rejects it.
- The cheaper "reference" billing rate only triggers when you attach reference video. Image and audio references bill at the full text rate. Easy to misread, expensive to assume.
- With video input there is a minimum billing floor of roughly 5/3 of the output seconds, and input seconds count toward the bill. Trim your reference clips.
- The vendor supports duration=-1 (model picks the length), but there is no way to bill an unknown duration up front, so we could not expose it. Same reason the video-edit mode is not available in v1.
- No seed parameter. Two identical requests give two different videos.

Model page with playground and full parameter reference:
https://reapi.ai/models/seedance-2-5
https://reapi.ai

If you try it and hit an edge case I did not list, reply here. Genuinely curious what breaks first.