Imagen to Nano Banana Migration: The June 2026 Prompt Masterclass

Google will shut down every Imagen model on June 24, 2026 through Firebase AI Logic, and the Gemini API follows with an August 17, 2026 cutoff. If your prompts still call imagen-4.0-generate-001, they stop returning images this month. You need a migration plan, and you need it now.

The good news reads better than the warning. Google built Nano Banana 2 (Gemini 3.1 Flash Image) to absorb Imagen's workload and then add skills Imagen never had. You get web grounded infographics, precise in image text, translation, 4K resolution, and character consistency across five subjects. The tradeoff is that your request shape changes, and four Imagen parameters simply disappear.

This Masterclass walks you through the exact move, prompt by prompt, so your image pipeline survives the shutdown and comes back stronger.

What Actually Shuts Down and When

The retirement date depends on which Google surface you use, and that split confuses most teams. Firebase AI Logic posts a hard June 24, 2026 shutdown for all Imagen models. The Gemini API deprecations page lists August 17, 2026 for the same endpoints, with gemini-3.1-flash-image named as the replacement. Treat the earlier date as your real deadline, because Firebase powered most mobile and web app image calls.

Three Imagen endpoint IDs retire on the same schedule: imagen-4.0-generate-001, imagen-4.0-fast-generate-001, and imagen-4.0-ultra-generate-001. Google released Nano Banana 2 on February 26, 2026, so the replacement has already shipped across Vertex AI, Flow, and Google Ads. You are not migrating to a preview. You are migrating to the new default.

The Model ID Translation Table

You cannot migrate prompts until you swap the model name in your code. Use this table as your single source of truth.

Notice the method change. Imagen used generateImages. Nano Banana uses generateContent, because the image model now lives inside the Gemini content pipeline. Your old prompt text still works, but the wrapper around it must change.

Four Parameters That Break Overnight

Firebase documents four Imagen parameters that Nano Banana does not support, and you must remove them before your calls will succeed.

negativePrompt is gone. Negative prompts were already a legacy feature after imagen-3.0-generate-002, and no Imagen 4 model used them either. If your prompts lean on exclusion phrasing, rewrite them as positive instructions.

imageFormat is gone. Nano Banana always returns PNG. You handle format conversion on your end if you need WebP or JPEG.

numberOfImages is gone. Nano Banana returns a single image per call. To generate four variants, you run the call in a loop. Candidate count does not work as a workaround.

personGeneration is gone. Nano Banana allows generating images of people by default, so the safety filter toggle no longer applies.

If your migration skips these four removals, your API calls fail with parameter errors before they ever reach the model.

Three Prompts That Get Better After Migration

Here is where the migration stops feeling like loss and starts feeling like an upgrade. Nano Banana 2 brings capabilities Imagen 4 never offered, and your prompts can lean into them immediately.

Web grounded infographics. Nano Banana 2 pulls from Gemini's real world knowledge and live web search to render data accurately. Try this prompt: "Create a flat lay infographic depicting the water cycle, labeled stages, modern layout, blue and white palette." Google used this exact prompt in their launch demo, and the model rendered accurate labels and arrows on the first pass.

Localized text and translation. You can ask the model to generate and translate text inside the image. Try: "A museum sign that reads Native Wildlife in English, with accurate Spanish and French translations below, clean sans serif typography." Imagen 4 garbled text like this. Nano Banana 2 handles it because it treats text as rendered language, not as a texture.

Character consistency across scenes. Nano Banana 2 holds resemblance for up to five characters and the fidelity of up to 14 objects in a single workflow. Try: "Storyboard of four panels showing the same astronaut farmer planting corn on Mars, consistent face and suit across all panels, golden hour lighting." This prompt would have required reference image stitching on Imagen. On Nano Banana 2, a single text prompt carries the consistency.

A 30 Minute Migration Checklist

Run this sequence before the June 24 deadline and you will not lose a single day of generation.

First, audit every call site that references an imagen model ID and swap it to gemini-3.1-flash-image or gemini-3-pro-image. Second, replace generateImages with generateContent and update your response parser to read content parts instead of an image response object. Third, delete the four unsupported parameters from your request builder. Fourth, run a same prompt proof set, the same ten prompts across both old and new models, and visually confirm parity. Fifth, escalate any failed prompts to Nano Banana Pro before you conclude the model cannot handle them.

FAQ

When does Imagen shut down? Firebase AI Logic shuts down all Imagen models on June 24, 2026. The Gemini API follows on August 17, 2026.

What replaces Imagen 4? Nano Banana 2 (gemini-3.1-flash-image) is the default replacement. Nano Banana Pro (gemini-3-pro-image) handles premium text, layout, and 4K work.

Does Nano Banana support negative prompts? No. Negative prompts are not supported on any Nano Banana model, and they were already legacy on Imagen 4.

Can I generate multiple images in one call? No. Nano Banana returns one image per call. Run the call in a loop to generate variants.

Is Nano Banana 2 free? It is the default model in Google Flow at zero credits. Vertex AI and the Gemini API bill per image, with pricing set by Google Cloud.