Blog · 2026-10-09

Nano Banana 2.1 vs GPT Image 2.5: Same Prompts, Side by Side (2026)

Nano Banana 2.1 and GPT Image 2.5 are the two image models most teams are choosing between this autumn: Google's efficient Flash-class model, released on 6 October 2026, and OpenAI's GPT Image 2.5, released on 9 September 2026 in two tiers, Flare and Sunburst. We ran the same five prompts through Nano Banana 2.1 and through GPT Image 2.5 Sunburst at high quality, with the same reference images, and put the results side by side below without retouching.

Disclosure: we run apimodels.app, an API platform that serves both models under one key, and every test below was run there.

The short answer

Pick Nano Banana 2.1 for volume work, ultra-wide or very tall formats, and edits where the rest of the image must not move. Pick GPT Image 2.5 Sunburst for close-up hero images, dense typography and anything that needs a transparent background. On our five prompts both models spelled every string correctly, so text accuracy alone did not separate them.

What each model is

Nano Banana 2.1 is Google's high-efficiency image generation and editing model, built on Gemini 3.6 Flash. Google calls it the more efficient counterpart to Gemini 3 Pro Image. It outputs 1K, 2K or 4K in 15 aspect ratios, including the new 1:4, 4:1, 1:8 and 8:1, and on apimodels.app it accepts up to 10 reference images. Google's model card reports 1106 on multi-character editing and 0.521 on infographic factuality, against 978 and 0.179 for Nano Banana 2.

GPT Image 2.5 is OpenAI's image model, offered as two API models with the same feature set: gpt-image-2.5-flare, the faster default tier, and gpt-image-2.5-sunburst, which spends more time per image on fine detail. Both edit only the region you point at, hold a character across rounds of edits, return native transparent PNG, and cover six aspect ratios (21:9, 16:9, 4:3, 1:1, 3:4, 9:16). Price depends on resolution and quality, from low to max.

Price per image on apimodels.app

                         1K        2K        4K
Nano Banana 2.1          $0.024    $0.04     $0.064
GPT Image 2.5 Sunburst   $0.03     $0.04     $0.16     (high quality)
GPT Image 2.5 Flare      $0.02     $0.025    $0.045    (medium quality)

At 2K, Nano Banana 2.1 and Sunburst at high quality cost the same $0.04. At 4K, Sunburst high is $0.16 against $0.064. Flare at medium quality is the lowest-priced option of the three at every tier, which is worth knowing if you need volume and Flare's quality is enough. Failed requests are not charged on apimodels.app.

How we tested

Five prompts, one run each per model, 2K output, GPT Image 2.5 Sunburst at high quality. Edits and merges used identical reference images on both sides. Nothing was retouched or cherry-picked from multiple tries. The characters, the restaurant and the HEARTH & CLAY logo were invented for the test. One run per prompt is a sample, not a benchmark, so treat the differences below as tendencies.

Test 1: a bilingual poster

The prompt asked for a noodle restaurant poster with three strings: "Winter Specials" in large brush lettering, "冬季限定" below it, and "Open daily 11:00–22:00 · 18 Lantern Street" along the bottom. Both models placed all three correctly, including the Chinese line and the en dash, and neither added stray text. GPT Image 2.5 Sunburst produced a richer, cinematic street scene with a painted porcelain bowl; Nano Banana 2.1 produced a flatter illustration that is closer to a menu design. Here the difference is style, not accuracy.

Test 2: an infographic

Six stages from harvest to brew, each with a one-word label, plus a note under the roasting step. Both models got all six labels and the note right. GPT Image 2.5 Sunburst drew one straight arrow between each pair of stages, so the flow reads cleanly; Nano Banana 2.1's arrows double back between the first stages, although every illustration matches its label and it added people at each step. For a slide where the reader has to follow the order at a glance, Sunburst's version is the one we would ship.

Test 3: one character, a new scene

Both models received the same turnaround sheet of an invented courier, Mira, and were asked to keep her face, hair, glasses, jacket, shorts, sneakers and bag exactly the same while she rides through a night market in the rain. Both kept every listed detail, including the orange shoulder patch. GPT Image 2.5 Sunburst rendered deeper lighting and wet-street reflections, and its shop signs are real, readable words; Nano Banana 2.1 stayed closer to the sheet's flat drawing style, and its signs are decorative pseudo-lettering. If background text will be read, that matters.

Test 4: swap one object

Replace the vase with "a small clear glass bottle holding a single sprig of eucalyptus" and keep the table, chairs, window, curtains, floor, light and camera angle as they are. Both models changed only the vase. GPT Image 2.5 Sunburst followed "a single sprig" literally; Nano Banana 2.1 put three or four sprigs in the bottle. Everything else in both edits lines up with the original.

Test 5: merge a logo into a product photo

Two references, a teapot photograph and a logo, with the instruction to press the logo into the clay and keep the teapot, the slate, the light and the background unchanged. Both pressed a legible HEARTH & CLAY stamp into the curve of the pot. Nano Banana 2.1 kept the original framing exactly; GPT Image 2.5 Sunburst reproduced the logo's double ring more faithfully but re-framed the shot slightly, with the teapot larger in the frame. For SKU variants that must line up pixel for pixel, Nano Banana 2.1's behaviour is the safer one.

What only one of them can do

Ultra-wide and very tall formats are Nano Banana 2.1 only: 8:1, 4:1, 1:4 and 1:8 are not among GPT Image 2.5's six ratios. The banner above is 5856×704 at the 2K tier. A caveat from our own runs: on the first attempt, with small lettering, Nano Banana 2.1 garbled one word; asking for lettering about a fifth of the banner height fixed it. Transparent PNG is GPT Image 2.5 only; Nano Banana 2.1 has no transparent-background option in its API.

Speed

We are not ranking speed from these five runs, because some of them were retried across upstream routes during the test. Over a longer sample on apimodels.app, Nano Banana 2.1 typically returns in about 15 to 30 seconds at 1K and 2K, and our earlier 40-call test of GPT Image 2.5 measured a median of 24.8 seconds for Flare and 40.0 seconds for Sunburst. If someone is waiting on screen, Nano Banana 2.1 or Flare is the safer choice.

Which to choose

Nano Banana 2.1: product shots and listings in volume, social graphics, labelled diagrams, ultra-wide banners and tall stories, and edits or logo merges where everything outside the change must stay exactly where it was.

GPT Image 2.5 Sunburst: hero images that will be seen up close, scenes where background text must be real, layouts with dense typography, and anything that needs a transparent background. GPT Image 2.5 Flare: the same features at lower latency and, at medium quality, the lowest price per image of the three.

When this comparison does not apply

If you need Nano Banana 2.1's thinking levels, Google Search grounding or all 14 reference images, call Google's Gemini API directly; apimodels.app exposes up to 10 references and does not pass those options through yet. If your images need a full paragraph of copy or very small print, neither model is reliable at 1K; render at 2K or 4K or add the text in a design tool. And because each prompt ran once, a different prompt can reverse a narrow result.

Both models are on apimodels.app with one API key: the model ids are nano-banana-2-1, gpt-image-2.5-sunburst and gpt-image-2.5-flare, so switching is a one-string change. The nine Nano Banana 2.1 use cases these test images came from, each with its full prompt, are on the Nano Banana 2.1 model page.

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