Gemini 3 Pro Image parameters

Pro uses the same Gemini-native body as Flash, with different YingTu prices and a stronger reason to consider asynchronous execution for large output.

Field	Value for this model
Model path	`gemini-3-pro-image`
`imageSize`	`1K`, `2K`, or `4K`; omitted means 1K
`aspectRatio`	Optional; `1:1` was verified at 1K and 4K
`responseModalities`	Include `IMAGE`; `TEXT` is optional
`candidateCount`	Omit or use `1`
1K / 2K / 4K price	USD 0.050 / USD 0.050 / USD 0.090

{
  "contents": [{
    "role": "user",
    "parts": [{"text": "A precise exhibition poster with a disciplined grid"}]
  }],
  "generationConfig": {
    "responseModalities": ["TEXT", "IMAGE"],
    "imageConfig": {"aspectRatio": "1:1", "imageSize": "4K"}
  }
}

Plan for Base64 size

The verified 4096 × 4096 JPEG contained roughly 7.4 MB of decoded image data; the JSON Base64 string was larger. Set client, proxy, and log limits accordingly. Do not retain full response bodies in ordinary application logs. For a caller with a short timeout, submit the same body to :asyncGenerateContent and move the completed image into storage you control.

Editing input

Use inlineData for a source image and preserve its real MIME type. The live 1K edit returned JPEG output and optional text may still appear before it.

A 4K request is billed at the 4K tier even when the prompt fails to use the extra resolution effectively. Validate at 1K or 2K before scaling 4K traffic.

​Plan for Base64 size

​Editing input

Plan for Base64 size

Editing input