Google has recently added Nano Banana Pro to its offerings. This article performs several tests on the API itself and the new capabilities of the model.

Related articles:

  1. Gemini "Nano Banana" image editing capability
  2. Gemini "Nano Banana" generally available

API Updates

  1. The model name is gemini-3-pro-preview. You can use it with the generateContent or streamGenerateContent endpoints.
  2. This model enforces a mandatory thinking process. The content parts would return the thoughtSignature, which must be stored. Conversation could not continue without the signature being attached as part of the input.
  3. It is possible to specify the image output size, such as 1K, 2K, or 4K. Sample:
{
   ......
    "generationConfig": {
        "maxOutputTokens": 32000,
        "imageConfig": {
            "aspectRatio": "16:9",
            "imageSize": "1K"
        },
        "thinkingConfig": {
            "thinkingBudget": 3000
        }
    }
}

Test #1 - 4K Image

The first test is a simple, straightforward request to generate an image based on a given prompt. The streaming takes 3 minutes to complete, and a JPEG image is received.

Check the image's metadata, and we can see it produced a 4K image.

Test #2 - With reference input images

The model allows up to 14 input images. In this test, we provide several images as a reference and observe how they are being used in the output.

The output looks great! Especially since it is done in 4K and a 16:9 ratio.

(This is a scaled-down version of the original output.)

Test #3 - Conversation & Image editing

In this test, we first generate an image, then request an edit to it.

Create a teddy bear image, sit behind the glass in a toy store. street view: modern tokyo. 
slightly cloudy. only a few ppl on the streets. no cars.

add some Christmas decoration around the bear. keep the street unchanged.

Test #4 - Combination of realistic & imaginary/illustrative

In the last test, we asked the model to generate an image of a computer screen showing a shooting game. 

Test #5 Combining Math & Handwriting Imitation

Solve this equation and write the steps with similar handwriting on the paper.

It returns a solution with the correct answer, written in a similar handwriting style.

Things to take note of

  1. Unlike the original Nano Banana, the new Pro model takes a much longer time (E.g., 2 to 4 minutes) to complete the request. It is recommended to use the streaming endpoint in a background process.
  2. If you have a restriction on file size (either firewall, server, or app level), remember to increase the value. The 4K image is huge; for example, a 16:9 image is around 8MB each.
  3. The Pro model utilises Gemini 3 Pro thinking capability. This is mandatory, and it increases the usage of tokens.
  4. The size of thoughtSignature can be huge. We have seen a range of hundreds of KB to a few MB. If your use case does not require a conversation, you should discard them without saving the signature.