Imagen 4 vs Nano Banana 2.1

TL;DR

Need "resolution options (1K/2K/4K), reference images, jpg / png output"? Use gemini-nano-banana-2.1. Need "three fixed tiers, stable materials and lettering, straight text-to-image"? Use Imagen 4 (imagen-4.0).
The hardest number is the price gap: standard Imagen 4 at $0.06 versus NB2.1 1K at $0.022 — $0.038 more per image, $60.00 versus $22.00 at 1,000 images. Even NB2.1 4K at $0.058 sits below Imagen 4 Ultra at $0.09.
Both are live on HiAPI: the Imagen 4 page and the Nano Banana 2.1 page, one shared /v1/tasks endpoint, 200 free credits on signup.

At a glance

	Imagen 4 (`imagen-4.0`)	`gemini-nano-banana-2.1`
Role	Pure text-to-image in three tiers (plus Fast / Ultra)	Text-to-image plus reference mixing
References	Not accepted	`image_input` up to 10, optional
Resolution	No resolution parameter	1K / 2K / 4K, default 1K
Aspect	`aspect_ratio` required, 6 options	`aspect_ratio` 15 options incl. auto, default auto
Output format	No format parameter	`output_format` jpg / png, default jpg
Price (per image)	Fast $0.03; standard $0.06; Ultra $0.09	1K $0.022; 2K $0.036; 4K $0.058
Tier structure	Three model IDs, one calling convention	One model, resolution inside
Best for	Delivery-grade output, material- and lettering-critical frames	Resolution-sensitive, reference-driven, png-direct pipelines

HiAPI current prices, checked October 21, 2026. Pay for successful images; failures refund in full; references are free.

Same prompt, both models, real outputs

One prompt each — Imagen 4 at standard, NB2.1 at 1K — with matching aspect ratios, one render each.

Pair A: product still (1:1)

Ceramic teapot and two cups on a wooden tray; soft morning light; minimalist product photo

Imagen 4 (standard $0.06)	`gemini-nano-banana-2.1` (1K $0.022)

Left: imagen-4.0, 1:1, 1024×1024, WebP, $0.06. Right: gemini-nano-banana-2.1, 1:1, 1K (1024×1024), png, $0.022. Same pixels in this pair, different formats.

Generate with Imagen 4 → | Generate with Nano Banana 2.1 →

What you can see in pair A:

The subject holds: a teapot, two handleless cups, a wooden tray, a pale setting with one soft light.
The pot and props differ: Imagen's is a round side-handled pot against a plain backdrop, a still-life-table feel; NB2.1's is a loop-handled pot with speckled glaze, a cloth beside the tray, and a blurred interior-window background.

Pair B: documentary portrait (3:4)

Elderly fisherman mending nets on a harbor pier; golden hour; documentary portrait

Imagen 4 (standard $0.06)	`gemini-nano-banana-2.1` (1K $0.022)

Left: imagen-4.0, 3:4, 864×1152, WebP, $0.06. Right: gemini-nano-banana-2.1, 3:4, 1K (896×1200), png, $0.022. Same prompt, one render each.

Generate with Imagen 4 → | Generate with Nano Banana 2.1 →

What you can see in pair B:

The person and action hold: a white-bearded fisherman mending nets on the pier, golden-hour side backlight, vertical documentary frame.
Seating and dress differ: Imagen has a blue plastic stool and a grey cap; NB2.1 has a wooden crate, a knitted hat, and a small knife in the right hand.
Prop density differs: NB2.1 stacks lobster cages and crates beside him with nets spread wider; Imagen keeps the ground lighter.

Both pairs match on aspect and differ on format (WebP vs png); pixel sizes are identical in pair A (1024×1024) and close-but-unequal in pair B (864×1152 vs 896×1200) — that's the endpoints themselves, so keep it in mind at full size.

Choosing by scenario

E-commerce and social volume: gemini-nano-banana-2.1 — $0.022 per 1K image, $22.00 per thousand, with references for style control.
Delivery-grade output with material detail and in-image lettering: Imagen 4 standard or Ultra.
Pipelines that need png / jpg straight out: NB2.1 (output_format is explicit); Imagen 4 has no format parameter, so conversion adds a step.
4K on a budget: NB2.1 4K at $0.058 undercuts Imagen 4 Ultra at $0.09 — test on your subject before committing.
Imagen 4 scene templates live in the prompt guide; tier details in the pricing page.

Switching cost: change model and input only

Both models POST to /v1/tasks with the same key and polling:

{
  "model": "imagen-4.0",
  "input": {
    "prompt": "Ceramic teapot and two cups on a wooden tray; soft morning light; minimalist product photo",
    "aspect_ratio": "1:1"
  }
}

{
  "model": "gemini-nano-banana-2.1",
  "input": {
    "prompt": "Ceramic teapot and two cups on a wooden tray; soft morning light; minimalist product photo",
    "aspect_ratio": "1:1",
    "resolution": "1K",
    "output_format": "png"
  }
}

Imagen 4 requires only prompt and aspect_ratio; NB2.1 takes resolution and output_format explicitly and follows them — nothing else in your code moves.