Gemini 3.1 Flash Image parameters - YingTu API Docs

Flash accepts the shared Gemini-native contents body and three YingTu billing tiers. Put resolution inside generationConfig.imageConfig.

Field	Value for this model
Model path	`gemini-3.1-flash-image`
`imageSize`	`1K`, `2K`, or `4K`; omitted means 1K
`aspectRatio`	Optional; `1:1` was verified at 1K and 2K
`responseModalities`	Include `IMAGE`; `TEXT` is optional
`candidateCount`	Omit or use `1`
1K / 2K / 4K price	USD 0.025 / USD 0.037 / USD 0.055

{
  "contents": [{
    "role": "user",
    "parts": [{"text": "An editorial product scene with crisp typography space"}]
  }],
  "generationConfig": {
    "responseModalities": ["TEXT", "IMAGE"],
    "imageConfig": {"aspectRatio": "4:3", "imageSize": "2K"}
  }
}

Choose a resolution deliberately

1K is the lowest-cost default for thumbnails, iteration, and most app UI.
2K provides more working pixels for editorial and product assets.
4K is the highest YingTu tier and should be selected only when the delivery really uses the additional pixels.

The price is attached to the requested tier, not the output file’s byte size. Do not send lowercase size values or top-level resolution fields.

Editing input

Add inlineData beside the instruction. The verified edit accepted a JPEG source and returned a 1024 × 1024 JPEG at 1K.

{
  "contents": [{
    "role": "user",
    "parts": [
      {"text": "Keep the product geometry and change the background to pale blue"},
      {"inlineData": {"mimeType": "image/jpeg", "data": "BASE64_SOURCE_IMAGE"}}
    ]
  }],
  "generationConfig": {
    "responseModalities": ["TEXT", "IMAGE"],
    "imageConfig": {"aspectRatio": "1:1", "imageSize": "1K"}
  }
}

Actual output encoding is response data. Read mimeType; do not infer JPEG from the model ID.