Ideogram 4.5 vs Nano Banana 2 for multi-turn edits: cost per turn

Ideogram's launch post for 4.5 on 2026-09-30 claims it is its most precise edit model, with multi-turn edits that do not pile up artifacts. That is a claim about quality, and it is worth testing against the model you use now. Sume lists both Ideogram 4.5 and Nano Banana 2 as edit-capable, so one script can run the same chain through each.

Run the same chain through both

Each turn feeds the previous output URL back in as the new source. After six turns, compare the final image with the first on a region that was never meant to change. The script prints the cost and a drift score per model.

import io, os, requests
import numpy as np
from PIL import Image

H = {"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"}
START = "https://example.com/shelf.jpg"
STEPS = ["Make the mug blue.", "Add a plant on the left.", "Make the wall warmer."]

def load(url):
    return Image.open(io.BytesIO(requests.get(url).content)).convert("RGB")

for model in ["ideogram/ideogram-v4.5", "google/nano-banana-2"]:
    url, cost = START, 0.0
    for step in STEPS:
        r = requests.post("https://api.sume.com/v1/images", headers=H, timeout=90, json={
            "model": model, "prompt": step + " Keep everything else unchanged.",
            "input_references": [{"type": "image_url", "image_url": {"url": url}}]})
        r.raise_for_status()
        url, cost = r.json()["data"][0]["url"], cost + r.json()["usage"]["cost"]
    a, b = load(START), load(url).resize(load(START).size)
    box = (0, int(a.height * 0.6), a.width, a.height)
    d = np.abs(np.asarray(a.crop(box), float) - np.asarray(b.crop(box), float)).mean()
    print(model, round(cost, 4), round(d, 2))

How to read the result

The bottom 40% is a stand-in for an area your prompts never named; pick the real one for your photos. A lower score means less drift, and a flat score across turns means the chain is stable. Ideogram's claim is its own, and this is the way to check it on your images. The earlier post on four rounds for 30 cents has the Ideogram-only costs.