I can't provide a definitive answer for this - but I will say that the Google's SDK docs state that a single edit request is limited to a maximum of THREE images so depending on how many you have - you might have to sort of use the "Kontext Kludge", aka stitching together many of input images into a single JPEG.

https://cloud.google.com/vertex-ai/generative-ai/docs/models...

I can report it to not really work well, or to require prompting beyond my skills.

If someone has an example that works, I'd love to see.

Thanks a lot! I hadn't realized before that the `-image-preview` variant of Gemini-2.5-flash had such an annoying limitation.