Runway Gen-4.5 vs Seedance 2.0: inputs, length and price

On Runway's API, Gen-4.5 (gen4.5) makes 2–10 second clips from a prompt or a first-frame image and costs 12 credits a second. Seedance 2.0 (seedance2) makes 4–15 second clips from text, images or video, takes image, video and audio references, generates audio by default, and costs 36 to 150 credits a second by resolution. Gen-4.5 is Runway's own model; Seedance 2.0 is ByteDance's, which Runway also sells.

Every Runway fact below comes from Runway's own developer docs, read on 2026-09-28 and listed under Sources. Which one makes the better-looking clip is not answered here: run the same prompt on both. The Sume section uses Video generation.

How do Gen-4.5 and Seedance 2.0 differ on Runway?

Runway's request bodies are keyed on model, so a body written for one is not valid for the other. Its primer says seedance2 “adds audio, references, referenceVideos, and referenceAudio” to what gen4.5 takes (Runway Dev context).

What does a 10-second clip cost on Runway?

Runway sells credits at $0.01 each (pricing). A 10-second clip is 120 credits ($1.20) on gen4.5, and on seedance2 it is 360 credits ($3.60) at 480p or 720p, 400 credits ($4.00) at 1080p, or 1,500 credits ($15.00) at 4K. On seedance2, duration: "auto" is billed at the variant maximum up front, and unused credits are refunded after the generation finishes (API reference). Gen-4.5's ProRes, 10-bit and HDR outputs add a per-second surcharge, and Runway says those formats are being enabled progressively per account.

Is Seedance 2.0 a Runway model?

No. Seedance 2.0 comes from ByteDance Seed, whose page describes it as supporting “text, image, audio, and video inputs” (Seedance 2.0). Runway's changelog dates Gen-4.5 on its API to February 10, 2026 and Seedance 2.0 to May 28, 2026 (complete docs). Runway API Seedance covers all four Seedance ids on Runway.

Can I use Seedance 2.0 without Runway?

Yes. On Sume it is seedance-2 on POST /v1/videos: 4–15 seconds at 480p, 720p or 1080p, first and last frames, image, video and audio references, and optional audio (Video generation). It is priced per 1,000 video tokens at $0.0175 after Sume's × 1.25, so a 10-second 720p 16:9 clip reserves $3.78, plus a 5.5% agent fee by default (API pricing). Runway's Gen models are not in Sume's catalog today. Seedance tokens explains the token math.

Which should I pick?

• Pick Gen-4.5 if you want Runway's own model, 2-second clips, or ProRes, 10-bit or HDR delivery.
• Pick Seedance 2.0 if you need clips over 10 seconds, video or audio references, generated audio, or 4K on Runway.
• Pick a multi-model API if Seedance is one of several models your code calls on one balance.
• Either way, compare the same length and resolution: both price by the second, Seedance also by resolution.