Gemini 2.5 Flash Image parameters

Use the exact model ID in the request path:

gemini-2.5-flash-image

This model uses the documented Gemini request body with one critical difference: generationConfig.imageConfig.imageSize must be absent.

Output controls

Field	Value through this API
`responseModalities`	Include `IMAGE`; `TEXT` is optional
`candidateCount`	Omit or use `1`
`imageSize`	Omit
`aspectRatio`	Optional; choose one value below
Output tier	Approximately 1K
Top-level `n` or `resolution`	Not supported

Supported ratios:

1:1   2:3   3:2   3:4   4:3
4:5   5:4   9:16  16:9  21:9

The ratio list is the current public model contract. Requests should use only these values.

Minimal generation body

{
  "contents": [{
    "role": "user",
    "parts": [{"text": "A small museum label beside a ceramic sculpture"}]
  }],
  "generationConfig": {
    "responseModalities": ["TEXT", "IMAGE"],
    "imageConfig": {"aspectRatio": "4:3"},
    "candidateCount": 1
  }
}

Editing input

Put the instruction and source bytes in the same parts array. Add another inlineData part for each additional reference:

{
  "contents": [{
    "role": "user",
    "parts": [
      {"text": "Keep the sculpture and replace only the wall color"},
      {
        "inlineData": {
          "mimeType": "image/png",
          "data": "BASE64_SOURCE_IMAGE_1"
        }
      },
      {"inlineData": {"mimeType": "image/jpeg", "data": "BASE64_SOURCE_IMAGE_2"}}
    ]
  }],
  "generationConfig": {
    "responseModalities": ["TEXT", "IMAGE"],
    "imageConfig": {"aspectRatio": "4:3"},
    "candidateCount": 1
  }
}

Use raw Base64 without a data URL prefix, and match mimeType to the actual source bytes. Unified asynchronous editing accepts 1–16 images, with a 20 MiB decoded limit per file and 64 MiB total. A fixed maximum source-image byte or pixel size is not currently published. Total request-body, proxy, and upstream limits may differ; reduce the source image if the API returns HTTP 413, and contact API support before relying on a guaranteed production envelope.

Do not send imageSize: "1K". The approximately 1K output does not make that field valid for this model.

Copy the complete examples

Use self-contained synchronous, asynchronous, and editing requests.

Review migration choices

Move to Lite or Flash according to the required output tier.

​Output controls

​Minimal generation body

​Editing input

Copy the complete examples

Review migration choices

Output controls

Minimal generation body

Editing input