9-second vertical story ad on Seedance 2.5, and the marginal second

A 9-second 9:16 Seedance 2.5 clip costs $2.42 at 480p, $5.20 at 720p and $12.79 at 1080p on Sume. Seedance 2.5 is token-priced from resolution, seconds and aspect ratio (read 2026-10-09), so an odd length like 9 seconds is a straight multiple of the per-second rate.

Price of a 9-second story, by resolution

Instagram and TikTok story slots are vertical, and 9 seconds sits between the two lengths most guides price (5 and 10). Seedance 2.5 accepts every whole second from 4 to 30, so you can buy exactly the length the edit needs.

Submit a 9:16 clip

Set aspect_ratio to 9:16 and duration to 9. The same body works on POST /v1/videos with any of the three resolutions; only resolution changes the price by a large step.

import os, time, requests

API = "https://api.sume.com/v1/videos"
H = {"Authorization": "Bearer " + os.environ["SUME_API_KEY"]}
body = {"model": "seedance-2.5", "prompt": "Handheld shot of a barista pouring latte art, steam rising, warm window light", "duration": 9, "resolution": "720p", "aspect_ratio": "9:16"}
job = requests.post(API, headers={**H, "Idempotency-Key": "story-latte-001"}, json=body, timeout=60).json()
deadline = time.time() + 1800
while time.time() < deadline:
    time.sleep(30)
    job = requests.get(job["polling_url"], headers=H, timeout=60).json()
    if job["status"] == "completed":
        print(job["unsigned_urls"][0], job["usage"]["cost"])
        break
    if job["status"] in ("failed", "cancelled"):
        print(job["status"], job.get("error"))
        break

Why 9 seconds, not 8 or 10

Eight seconds at 720p 9:16 costs $4.62 and ten seconds costs $5.78. Nine falls in between at $5.20. The step is $0.5778 for each added second at 720p, and $1.4216 at 1080p.

That marginal second matters when you trim a cut. If your edit runs long by one second, dropping to the next shorter length saves exactly that step, with no bucket to fall into.

A three-variant test at 480p costs $7.25. One 1080p final costs $12.79. The final is about 1.8 times the whole test round, which is why the draft stage should settle the concept first.

What to check

• 9:16 and 16:9 cost the same at 720p and 1080p for this length; 9:16 is not a discount, it is just the shape of the placement.
• Stories play on a phone, so 480p is a legitimate proof stage. Step up only for the clip you will publish.
• Going from 720p to 1080p multiplies the price by 2.46; going from 480p to 720p multiplies it by 2.15.
• A 3-second clip is below the 4-second floor and is rejected at submit with the supported list in the error details.