Omni reference tokens follow list order: swap list, swap meaning

In a Gemini Omni Flash 1.1 reference request, <IMAGE_REF_0> means the first URL in reference_image_urls and <IMAGE_REF_1> the second, counted from 0 in list order. If you reorder the list but not the prompt, the prompt now describes the wrong picture, and the 8-second clip still costs $1.00 at 720p on Sume.

That is a cheap bug to make and an expensive one to find by eye. This post shows the numbering rule and a check that catches it before you submit (price from the Sume price tool, read 2026-10-09).

The numbering rule

Limits: up to 10 reference images and up to 3 reference videos of at most 3 seconds each. The catalog notes that reference media is sent before the prompt, which is why the numbering follows the list and not the prompt text.

A body where the order matters

Here the product is first and the hand is second. Swap the two URLs and <IMAGE_REF_0> becomes the hand.

{
  "model": "gemini-omni-flash-1.1",
  "prompt": "<IMAGE_REF_0> sits on a desk while <IMAGE_REF_1> picks it up",
  "reference_image_urls": [
    "https://example.com/product.png",
    "https://example.com/hand.png"
  ],
  "resolution": "720p",
  "duration": 8,
  "aspect_ratio": "9:16",
  "mode": "async"
}

A check before you submit

This function fails when a token points past the end of its list. It cannot tell whether the order is right, so keep the list and the prompt in one place in your code.

import re

def check(prompt, images, videos):
    for kind, items in (("IMAGE", images), ("VIDEO", videos)):
        for n in map(int, re.findall(rf"<{kind}_REF_(\d+)>", prompt)):
            if n >= len(items):
                raise ValueError(f"<{kind}_REF_{n}> but only {len(items)} {kind.lower()}s")

images = ["https://example.com/product.png", "https://example.com/hand.png"]
check("<IMAGE_REF_0> sits on a desk while <IMAGE_REF_1> picks it up", images, [])

What a mix-up costs

A wrong-order take is still a full take. At 720p an 8-second take is $1.00, and ten of them are $10.00. At 1080p, ten are $15.00. Test the order at 360p, where an 8-second take is $0.30.

Write the prompt and the list in one function so the pair cannot drift apart, and add the token check above to your tests.

Limits and gotchas

If the clip shows the right objects doing the wrong thing, look at the list order first.

• Edit requests use video_url, and it cannot ride with reference_*_urls. Tokens do not apply to an edit.
• reference_audio_urls is not supported on Omni.
• Omni 1080p for the same 8 seconds costs $1.50; the tokens work the same at every resolution.