Image Generation

Use phaseo:image_generation when the model should be able to create an image while it is answering. Phaseo exposes a managed tool to the model, executes the image request server-side, and feeds the image result back into the model loop.

Request

curl https://api.phaseo.app/v1/responses \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5-nano",
    "input": "Design a wide product concept image for a compact desktop synthesizer.",
    "tools": [
      {
        "type": "phaseo:image_generation",
        "parameters": {
          "model": "openai/gpt-image-2",
          "quality": "high",
          "aspect_ratio": "16:9",
          "output_format": "png"
        }
      }
    ]
  }'

Parameters

Parameter	Type	Description
`model`	string	Optional image-capable model ID. Defaults to `openai/gpt-image-2` when neither the tool nor tool call provides a model.
`quality`	string	Optional provider quality hint, such as `low`, `medium`, or `high`.
`size`	string	Optional image size hint.
`aspect_ratio`	string	Optional aspect ratio, such as `1:1`, `16:9`, or `9:16`.
`background`	string	Optional background mode hint.
`output_format`	string	Optional output format, such as `png`, `jpeg`, or `webp`.
`output_compression`	integer	Optional provider compression hint.
`moderation`	string	Optional provider moderation hint.

The model supplies the final prompt when it calls the tool. Tool-level parameters provide defaults and constraints for that call. The tool call may also send description instead of prompt. Phaseo treats description as a prompt alias for compatibility with model-generated image descriptions.

Tool Result

The result is returned to the model as JSON:

{
  "status": "ok",
  "model": "openai/gpt-image-2",
  "imageUrl": "https://...",
  "mime_type": "image/png"
}

Some providers return base64 image data instead:

{
  "status": "ok",
  "model": "openai/gpt-image-2",
  "b64_json": "...",
  "mime_type": "image/png"
}

Usage And Pricing

Image generation usage is included in the parent response usage when the image model reports token usage. Phaseo also records:

{
  "usage": {
    "server_tool_use": {
      "image_generation_requests": 1
    }
  }
}

Pricing cards can bill this with the server_tool_image_generation_requests meter. The underlying image model usage can still be billed through its normal model pricing.

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