16 references on GPT Image 2.5, 5 on Ideogram 4.5: read limits in code

On Sume, GPT Image 2.5 accepts up to 16 input_references and Ideogram 4.5 accepts 5 in total: the first is the image it edits and up to 4 more act as references. The reference limit is part of each model's catalog descriptor, so read it from GET /v1/images/models instead of hard-coding a number.

Two limits documented in the Image API page

Read the limit for every model

Each model's supported_parameters includes an input_references range descriptor with min and max. This script prints the maximum for every row. A max of 0 means text-only.

import os, requests

r = requests.get(
    "https://api.sume.com/v1/images/models",
    headers={"Authorization": f"Bearer {os.environ['SUME_API_KEY']}"},
    timeout=30,
)
r.raise_for_status()
for m in r.json()["data"]:
    ref = m["supported_parameters"].get("input_references")
    print(m["id"], ref["max"] if ref else 0)

Why the number matters

A reference-heavy edit can include a product shot, a logo, a hand pose and a background plate. With a 5-image cap you must merge or drop inputs, while a 16-image cap lets you pass them all. The extra input also counts toward GPT Image 2.5 pricing, since the docs state that admission includes estimated input tokens, so a 16-reference call can cost more than the 7-cent catalog figure.

Keep reference order stable between runs. The order is part of how the model is steered, and changing it is a common reason a rerun looks different.

Rules that apply to every reference

Reference URLs must be public HTTPS. Sume rejects localhost, private-network and non-HTTPS addresses before submission, so a signed URL on a private bucket works only if the host is reachable from the public internet. Each entry is an object of type image_url with the address under image_url.url. Ideogram 4.5 without references generates from text, and with references it edits the first image.

Plan a four-photo edit as an example. Four references on GPT Image 2.5 at high bill about 7 cents plus input tokens, and the same four on Ideogram 4.5 fit inside the 5-image cap, billing 8 cents at medium. A twelve-photo gift basket fits only on GPT Image 2.5. Write the limit check into your code once, so a thirteenth photo fails in your script instead of after you pay for a submission.