GPT Image 2.5 vs Nano Banana Pro: text, editing, references and sizes compared

GPT Image 2.5 and Nano Banana Pro are the flagship image models from OpenAI and Google, and neither wins everywhere. GPT Image 2.5 is the better fit when you need a transparent background, a masked edit, several images per request or an exact pixel size. Nano Banana Pro is the better fit for images built around text, for mixing up to 14 references while keeping up to 5 people consistent, and for 4K as a fully supported output tier. Both generate and edit, and both run through the same SeedRouter endpoint, so you can compare them on your own prompts with one key.

Every fact about the models below comes from OpenAI's and Google's own documentation, checked on September 29, 2026. Facts about the request bodies come from the SeedRouter API references for GPT Image 2.5 and Nano Banana Pro.

How do GPT Image 2.5 and Nano Banana Pro compare at a glance?

Each model has more than one ID on SeedRouter. GPT Image 2.5 Flare vs Sunburst covers the two OpenAI tiers, and Nano Banana 2 vs Pro vs Lite places Pro among Google's image models.

Is GPT Image 2.5 better than Nano Banana Pro?

Not across the board; each vendor aims its model at different work. OpenAI describes GPT Image 2.5 Flare as its fastest model "for high-quality, everyday image generation" and Sunburst as the one for "workflows where editing precision matters most". Google describes Nano Banana Pro as "the premium choice for the most complex visual tasks", best for "complex graphic design, high-fidelity product mockups, and factual data visualizations that require accurate text rendering".

Neither company's documentation compares the two models directly. The practical differences are in what each request can do, which the sections below go through. For a real answer on your own content, send the same prompt to both and compare.

Which is better at text in images?

Google makes the stronger claim. Its launch post calls Nano Banana Pro "the best model for creating images with correctly rendered and legible text directly in the image, whether you're looking for a short tagline, or a long paragraph", and says it can write text in multiple languages and translate text already in an image. Google's image guide adds one tip: the model "works best if you first generate the text and then ask for an image with the text".

OpenAI is more cautious about its own model. The limitations section of its image guide says that "although significantly improved, the model can still struggle with precise text placement and clarity", and that it "may have difficulty placing elements precisely in structured or layout-sensitive compositions".

So for posters, menus, infographics and labels where every word must be right, start with Nano Banana Pro, and check the result either way.

Which is better for editing an image?

Both edit from a text instruction plus reference images, but they offer different controls.

• GPT Image 2.5 takes a mask. Send the image in images and a PNG mask whose transparent area marks what to change. OpenAI's announcement says the model is better at changing only what you ask while keeping everything else the same, and positions Sunburst for edit-heavy work.
• Nano Banana Pro edits in conversation. There is no mask. You describe the change, and you can continue across turns: each result returns output.parts with a thoughtSignature you send back to keep editing. Google highlights localized edits, camera angle, focus, color grading and relighting.

Pick GPT Image 2.5 when the edit must stay inside a region you can draw. Pick Nano Banana Pro when the edit is a series of written instructions applied to the same image, one after another.

How many reference images can each model use?

Google's announcement says Nano Banana Pro can blend up to 14 images while "maintaining the consistency and resemblance of up to 5 people". OpenAI says GPT Image 2.5 keeps subjects from reference photos more recognizable than before, without a count per role.

On SeedRouter, references for both models are public image URLs; base64 and file uploads are not accepted.

What sizes and aspect ratios can each model make?

GPT Image 2.5 takes an exact size such as 1536x1024, or auto. Width and height must be multiples of 16, neither edge above 3840 pixels, the ratio between 1:3 and 3:1, and the total area within the documented range. OpenAI calls resolutions above 2560×1440 experimental.

Nano Banana Pro takes an aspectRatio from a fixed list of ten, from 1:1 to 21:9, and an imageSize of 1K, 2K or 4K. At 1:1, 4K is 4096×4096. You choose a ratio and a size tier, not exact pixels.

GPT Image 2.5 returns PNG or JPEG, set with output_format; Nano Banana Pro reports the format of each result in output.output_format. Only GPT Image 2.5 has a background: "transparent" setting, which needs PNG output.

Which one is faster?

Neither vendor publishes a comparable speed figure. OpenAI says GPT Image 2.5 Flare produces higher-quality images than GPT Image 2 with 50% lower latency, that Sunburst takes longer for more precision, and that complex prompts "may take up to 2 minutes". Google says Nano Banana Pro always thinks before it draws and can render up to two interim images while planning; thinking cannot be turned off.

For drafts, the GPT Image 2.5 API reference suggests quality: "low", since higher tiers take longer to render. Measure both on your own prompts before you commit a latency budget.

How do the API requests differ?

Both models use POST /v1/images/generations on SeedRouter and return a task ID that you poll at GET /v1/tasks/{id}. The request bodies differ. GPT Image 2.5 takes an OpenAI-style body:

curl https://api.seedrouter.ai/v1/images/generations \
  -H "Authorization: Bearer $SEEDROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-image-2.5-flare",
    "prompt": "An amber glass bottle on a cream background, studio lighting",
    "size": "1024x1024",
    "quality": "low"
  }'

Nano Banana Pro takes Google's generateContent body plus a model field:

curl https://api.seedrouter.ai/v1/images/generations \
  -H "Authorization: Bearer $SEEDROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemini-3-pro-image",
    "contents": [{"parts": [{"text": "A ceramic teapot on a linen tablecloth, soft window light"}]}],
    "generationConfig": {
      "responseModalities": ["IMAGE"],
      "imageConfig": {"aspectRatio": "16:9", "imageSize": "2K"}
    }
  }'

Google Search grounding, which Google lists for Nano Banana Pro, is not available on SeedRouter yet: a request with tools is rejected. Streaming and partial images are not offered for either model.

Which should you pick?

• Transparent PNGs, stickers and cut-outs: GPT Image 2.5.
• An edit limited to one region: GPT Image 2.5 with a mask; Sunburst when precision matters most.
• Several variations from one request: GPT Image 2.5, with n up to 10.
• Exact pixel dimensions for a layout: GPT Image 2.5.
• Posters, infographics, menus and translated text: Nano Banana Pro.
• A composition built from many references or several recurring people: Nano Banana Pro.
• 4K as a supported tier: Nano Banana Pro (GPT Image 2.5 accepts up to 3840 px per edge, but OpenAI calls sizes above 2560×1440 experimental).

Both models add provenance marks: Google adds a SynthID watermark to every image, and OpenAI uses C2PA metadata and an invisible watermark.

Frequently asked questions

Is Nano Banana Pro better than ChatGPT image generation?

It depends on the job. ChatGPT's image generation runs on OpenAI's Images 2.5, which the API offers as GPT Image 2.5. Nano Banana Pro has the stronger vendor claim for text in images and more reference roles; GPT Image 2.5 adds masks, transparent backgrounds and up to 10 images per request.

Is ChatGPT's image model the same as GPT Image 2.5?

They are the same generation. OpenAI launched ChatGPT Images 2.5 on September 8, 2026, and released GPT Image 2.5 Flare and Sunburst in the API the same day, saying Flare brings the same gains in quality, editing and speed.

Can I call both models with one API key?

Yes. On SeedRouter both use the same endpoint and the same key; you switch by changing model and the body shape shown above.

Which model can make a transparent background?

GPT Image 2.5, with background: "transparent" and PNG output. The Nano Banana Pro request has no background setting.

Which one costs less?

It depends on the ID and the size. Standard IDs of both models charge one flat price per delivered image, and Official IDs bill by token usage. The GPT Image 2.5 pricing guide and the Nano Banana pricing guide have the details, and each model page shows live rates.

Try both

Run the same prompt in the GPT Image 2.5 Playground and the Nano Banana Pro Playground, then check the GPT Image 2.5 API reference and the Nano Banana Pro API reference before you integrate. You top up once with no subscription, credits never expire, new accounts start with a small free balance, and a failed request is not charged.