AI thumbnail variants in one call: n=4, pick one, then polish

Use n: 4 with aspect_ratio: "16:9" to get four thumbnail options from one request, choose one by eye, then edit that single image to polish text or color. The Image API accepts n up to 10, but each model sets its own ceiling in the catalog (the docs example, Seedream 4.5, lists 1 to 4), so read the n range for your model from GET /v1/images/models before relying on four (Image API docs).

This beats four separate calls because you send one request, one response lists four URLs, and usage.cost shows the total in a single field.

Plan the two steps

Each step has a different job.

Code for both steps

The script prints four URLs, asks for a choice and runs the polish edit.

import os
import requests

H = {"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"}
U = "https://api.sume.com/v1/images"
M = "openai/gpt-image-2.5"

a = requests.post(U, headers=H, timeout=90, json={"model": M, "n": 4,
    "aspect_ratio": "16:9", "quality": "medium",
    "prompt": "YouTube thumbnail, surprised cook holding a giant pancake"})
a.raise_for_status()
urls = [d["url"] for d in a.json()["data"]]
for i, u in enumerate(urls):
    print(i, u)
b = requests.post(U, headers=H, timeout=90, json={"model": M,
    "aspect_ratio": "auto", "quality": "high",
    "prompt": "Same thumbnail, brighter colors, keep the composition",
    "input_references": [{"type": "image_url", "image_url": {
        "url": urls[int(input("pick: "))]}}]})
print(b.status_code, b.json())

When is n=4 wasteful?

If you already have a layout, skip the options and just edit. If text accuracy is the goal, a wide choice of compositions does not help, so move to a higher quality or a model with better text rendering. Four images cost four times one, and fal lists GPT Image 2.5 at $0.0060 for a 1024 square at low (read 2026-10-01, fal); Sume's own price is in the response.

What to ask the polish step for

Polish prompts work best when they change one thing: brighten the colors, make the headline larger, or move the subject. Name the thing to keep ('keep the face and the pancake') so the edit does not become a new image. If the polish drifts too far, go back to the picked option and try a second, smaller edit.

Limits

A 4-image call may exceed the 30-second sync wait and return a 202 job, in which case you poll the job, not the original call. Thumbnails shrink a lot, so view the pick at small size before polishing. YouTube's own size rules were not checked for this post.