You can set aspect ratios with NB2 Lite programmatically through Vertex [1]. I updated the program I use to help create all the images for GenAI Showdown, set the model ID to `gemini-3.1-flash-lite-image`, and was able to use aspect ratios like 16:9, 4:3, and others.

[1] - https://cloud.google.com/developers/vertex-ai