Runway API vs Seedance on BytePlus ModelArk

Runway API

OpenAPI 3.1, llms.txt and Markdown copies of every docs page. Gen-3 Alpha Turbo and Gen-4 Aleph were removed on 2026-07-30 with no prior notice in the changelog.

Seedance on BytePlus ModelArk

The video task API documents limits, error codes and per-model parameters in detail, with callbacks, a filterable task list and API keys restrictable by model and IP address. No status page, OpenAPI file or free video quota was found, the newest models need a USD 30 balance, and BytePlus model services are not sold in the United States.

Runway API

1. Send X-Runway-Version: 2024-11-06 on every request or it fails
2. Use the SDK's wait-for-output helper or poll GET /v1/tasks/{id} until SUCCEEDED or FAILED
3. Don't retry a SAFETY.* failure unchanged. It's moderation, not an outage
4. Take model IDs from the models page, not memory. Two were removed without notice on 2026-07-30
5. Copy outputs to your own storage. URLs expire within 24 to 48 hours

Seedance on BytePlus ModelArk

1. POST to /api/v3/contents/generations/tasks on ark.ap-southeast.bytepluses.com, then poll GET /contents/generations/tasks/{id} or pass callback_url. Callbacks need an answer within 5 seconds
2. Download the result at once. Video URLs last 24 hours, task records 7 days, and a Seedance 2.5 URL allows 100 downloads
3. Pass resolution, ratio and duration in the request body. Parameters appended to the prompt as --rs or --dur are weakly validated and may be ignored
4. On Seedance 2.5 set omni_reference_task_type to edit or extend so constraint errors arrive at submission. With auto they arrive after the task leaves the queue
5. Do not send reference images or video with real human faces to Seedance 2.5 or 2.0. Only a queued task can be cancelled with DELETE