Runway video_to_hdr alpha and ProRes 4444: what Sume returns

Runway's September 11, 2026 changelog says /v1/video_to_hdr now preserves the alpha channel of a source video, writing it as the A channel in EXR deliveries and delivering hdr_prores as ProRes 4444. Sume's video docs describe no alpha, HDR or ProRes output; a completed job gives you a file through unsigned_urls or the /content endpoint.

What changed in Runway's video_to_hdr?

From the changelog, read 2026-10-01: sources with alpha (ProRes 4444, WebM with alpha, RGBA codecs) are detected automatically, with no request parameter. The alpha is passed through unchanged and is not premultiplied. hdr10 and hlg cannot carry alpha and deliver the video without it, and pricing is unchanged.

What does a Sume video job return?

Per the video docs, once a job is completed the unsigned_urls array lists the content to download, and GET /v1/videos/{jobId}/content?index=0 fetches it with your API key. The request fields cover resolution, aspect ratio, frame images, generate_audio and a callback_url webhook; none selects a container, bit depth or alpha. Do not plan a keyed or compositing workflow on Sume output without checking the file you receive.

How do I get notified when the file is ready?

Pass callback_url in the request body; the docs say Sume POSTs to it once the job reaches a terminal state, and it must be HTTPS. Webhooks are signed, so verify them before trusting the payload.

What should I do if I need alpha?

Do that step in a tool built for it, with the source and delivery you control. For the related HDR and EXR question, see what Sume outputs for HDR and EXR; for images, see opaque versus transparent backgrounds.