Providers sometimes make curious choices. Take Nano Banana: Google wired it into the chat interface generateContent, not the image API’s predict.
This is counterintuitive especially if you’re using RubyLLM which makes you think in terms of actions like paint, instead of chat.
The good news is that RubyLLM makes it super easy to use once you know that quirk. Only caveat: as of writing this post, you need the latest trunk or v1.9+ in the future, because that’s where we taught it how to unpack inline file data from chat responses.
Wire It Up
chat = RubyLLM
.chat(model: "gemini-2.5-flash-image")
.with_temperature(1.0) # optional, but you like creativity, right?
.with_params(generationConfig: { responseModalities: ["image"] }) # also optional, if you prefer the model to return only images
response = chat.ask "your prompt", with: ["all.png", "the.jpg", "attachments.png", "you.png", "want.jpg"]
image_io = response.content[:attachments].first.source
That StringIO holds the generated image. Stream it to S3, attach it to Active Storage, or keep it in memory for a downstream processor.
Want a file?
response.content[:attachments].first.save "nano-banana.png"
That’s it. Chat endpoint, one call. Ship the image feature and go enjoy the rest of your day.
