Three model IDs go dark today. imagen-4.0-generate-001, imagen-4.0-ultra-generate-001 and imagen-4.0-fast-generate-001 reach their shutdown date on August 17, 2026 — fourteen months after Google shipped them. Google’s deprecations page, last updated August 13, lists all three with the same date and the same recommended replacement: gemini-3.1-flash-image.
This is not a Gemini API quirk. Firebase’s migration guide states the shutdown applies “across Google and for both the Gemini Developer API and Agent Platform Gemini API (formerly Vertex AI).” If your product generates images through Google, today is the day it stops — or the day it starts costing more.
Because the replacement is not a swap. It is a different model family, called a different way, at a different price, with fewer knobs. It also lands in a stretch where Google has been shipping replacement models faster than teams can adopt them.
The price move
Imagen 4 billed flat, per image: $0.02 Fast, $0.04 Standard, $0.06 Ultra. Gemini image models bill by output tokens, which Google converts to per-image equivalents on its pricing page. Gemini 3.1 Flash Image runs $0.045 for a 0.5K image, $0.067 at 1K, $0.101 at 2K and $0.151 at 4K.
Do the division. A team on Imagen 4 Standard moving to Flash Image at 1K pays 68% more per image. A team on Imagen 4 Fast pays 235% more. Firebase points Ultra users at gemini-3-pro-image instead, at $0.134 per 1K image — up 123% from Ultra’s $0.06.
At 100,000 images a month, an Imagen 4 Fast bill of $2,000 becomes $6,700. An Ultra bill of $6,000 becomes $13,400.
There is a floor, and it is worth knowing about. Gemini 3.1 Flash Lite Image costs $0.0336 per 1K image on standard, and $0.0168 on batch. Batch is the only route on Google’s published card that lands below Imagen 4 Fast. Everything else is an increase.
Our take: Deprecations get filed under engineering. This one is a line-item. Any team generating images at volume through Google should treat today as a pricing event first and a code change second — and should price Flash Lite and batch before defaulting to the model Google recommends.
What you lose in the move
The Firebase guide lists the Imagen configuration options that have no Gemini equivalent, and the list is longer than a migration note usually admits:
numberOfImages— not supported. Imagen 4 returned one to four images per call. Gemini image models always return a single image. Google’s stated workaround is to loop.imageFormat— not supported. Output is always PNG.addWatermark— not supported. Every generated image carries a SynthID watermark.personGeneration— not supported. Gemini image models allow generating people by default.negativePrompt— not supported, though Google notes this one has been dead sinceimagen-3.0-generate-002.
The call itself changes shape too. ImagenModel becomes GenerativeModel; generateImages() becomes generateContent() with a response modality of IMAGE. Anything wrapping the old method breaks rather than degrades.
Google’s own docs disagree
Here is the part worth checking twice. The deprecations table and the Imagen 4 model page both name gemini-3.1-flash-image as the replacement. The pricing page’s warning on the same models says to migrate to Gemini 2.5 Flash Image instead — a model the deprecations table shows shutting down on October 2, 2026, whose own listed replacement is gemini-3.1-flash-image-preview, which shut down on June 25, 2026.
Three Google pages, three answers, one of them pointing at a model that has been off for seven weeks. Anyone migrating off the pricing-page warning today would be migrating onto a six-week runway.
What to watch
- Whether the shutdown lands cleanly today. Google’s deprecations page calls its dates “the earliest possible dates on which a model might be retired” — Imagen 4 could linger.
- Gemini 2.5 model shutdowns in October, which sweep up
gemini-2.5-flash-imageon the 2nd. - Whether per-token image billing holds. Flat per-image pricing was easy to forecast; token-based pricing that scales with resolution is not.
- Whether rivals quote flat per-image rates at teams doing the migration math this week — including the open-weights camp, where licence terms carry their own tripwires.
- Google’s pattern of dates slipping in both directions, after a flagship that sat in preview months past its stated window.