Hy Image 3.5 Preview returns base64 PNG; Sume returns a URL

Tencent's Hy Image 3.5 Preview, as listed on OpenRouter, returns the image as base64 PNG. Sume's POST /v1/images works differently: the response holds data[].url, a Sume-hosted signed URL, and no inline base64. If your code decodes base64 today, the change is to download the URL instead. Sume does not list Hy Image 3.5 Preview, so the example below calls a model that Sume does list.

What each side returns

The OpenRouter listing for Hy Image 3.5 Preview (read 2026-10-08) says the output is an image in PNG format via base64, and that the response carries usage.cost, the USD charge for the call. Sume's Image API docs say the result payload is data[].url, not inline base64, because Sume already mirrors generated media and URLs keep responses small. In Sume's usage object, cost is the billed USD amount and token counts are 0 in v1.

Download the URL

The code posts a request, treats 202 as a job, and saves the file. The signed URL is the only place the bytes live, so fetch it soon after the job completes. The Content-Type header tells you the extension to use.

import os, requests

H = {"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"}
body = {
    "model": "bytedance-seed/seedream-5-lite",
    "prompt": "A paper boat on a calm lake, morning light",
    "aspect_ratio": "1:1",
}
r = requests.post("https://api.sume.com/v1/images", headers=H, json=body, timeout=60)
r.raise_for_status()
if r.status_code == 202:
    raise SystemExit("job envelope: poll the status_url from the body")
url = r.json()["data"][0]["url"]
img = requests.get(url, timeout=60)
ext = img.headers.get("content-type", "image/png").split("/")[-1]
open(f"out.{ext}", "wb").write(img.content)
print("saved", len(img.content), "bytes as", ext)

Handle the 202 case

Examine the status code, not the body shape. Sume's docs say 200 is the image response and 202 is the job envelope, and that slow configurations (4K, high quality, large n) are the most likely to degrade to 202. A 202 body carries status_url and result_url. Poll the status URL until the job is terminal, then fetch the result, which holds the artifacts with content_type and url.

If your pipeline expects bytes in the first response, wrap the call in a function that returns bytes after either path. The submit-then-poll pattern also works with a webhook for the terminal event, which means no polling loop is needed.

What not to carry over

Do not port a request field just because it exists upstream. Sume rejects a parameter that the selected model does not list with 400 unsupported_parameter, rather than ignoring it. Read GET /v1/images/models for the row you chose, and send only the fields in its supported_parameters.