Image Generation

Helicone’s AI Gateway supports image generation through models with native image output capabilities. Use the unified OpenAI-compatible API to generate images - the Gateway handles provider-specific translations automatically.

Image generation is currently supported for Nano Banana Pro (gemini-3-pro-image-preview) via Google AI Studio. Support for additional providers will be added in future updates.

Quick Start

Chat Completions
Responses API

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.HELICONE_API_KEY,
  baseURL: "https://ai-gateway.helicone.ai/v1",
});

const response = await client.chat.completions.create({
  model: "gemini-3-pro-image-preview/google-ai-studio",
  messages: [
    { role: "user", content: "Generate an image of a sunset over mountains" }
  ],
  max_tokens: 8192
});

// Access generated images
const images = response.choices[0].message.images;

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.HELICONE_API_KEY,
  baseURL: "https://ai-gateway.helicone.ai/v1",
});

const response = await client.responses.create({
  model: "gemini-3-pro-image-preview/google-ai-studio",
  input: "Generate an image of a sunset over mountains",
  max_output_tokens: 8192
});

// Access generated images from output
const messageOutput = response.output.find(item => item.type === "message");
const imageContent = messageOutput?.content.find(c => c.type === "output_image");

Configuration

To enable image generation:

Set the model to one that supports image output (currently gemini-3-pro-image-preview/google-ai-studio, also known as Nano Banana Pro)
Optionally configure image_generation to control aspect ratio and size

Chat Completions
Responses API

{
  model: "gemini-3-pro-image-preview/google-ai-studio",
  messages: [...],
  image_generation: {
    aspect_ratio: "16:9",
    image_size: "2K"
  }
}

{
  model: "gemini-3-pro-image-preview/google-ai-studio",
  input: "...",
  image_generation: {
    aspect_ratio: "16:9",
    image_size: "2K"
  }
}

image_generation

Parameter	Type	Description
`aspect_ratio`	string	Image aspect ratio (e.g., `"16:9"`, `"1:1"`, `"9:16"`)
`image_size`	string	Image resolution (e.g., `"2K"`, `"1K"`)

The image_generation field is optional. If omitted, the model uses default settings. However, if you specify image_generation, both aspect_ratio and image_size are required.

Handling Responses

Chat Completions

Streaming
Non-Streaming

When streaming, images arrive in chunks via the images delta field:

// Image chunks arrive in delta
{
  "choices": [{
    "delta": {
      "images": [{
        "type": "image_url",
        "image_url": {
          "url": "data:image/png;base64,iVBORw0KGgo..."
        }
      }]
    }
  }]
}

Non-streaming responses include images in the message:

{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "model": "gemini-3-pro-image-preview",
  "choices": [{
    "index": 0,
    "message": {
      "role": "assistant",
      "content": "Here's the image you requested:",
      "images": [{
        "type": "image_url",
        "image_url": {
          "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA..."
        }
      }]
    },
    "finish_reason": "stop"
  }],
  "usage": {
    "prompt_tokens": 12,
    "completion_tokens": 1024,
    "total_tokens": 1036
  }
}

Responses API

Streaming
Non-Streaming

Streaming events follow the Responses API format:

// Content part added for image
{
  "type": "response.content_part.added",
  "item_id": "msg_abc123",
  "output_index": 0,
  "content_index": 0,
  "part": {
    "type": "output_image",
    "image_url": ""
  }
}

// Content part done with full image
{
  "type": "response.content_part.done",
  "item_id": "msg_abc123",
  "output_index": 0,
  "content_index": 0,
  "part": {
    "type": "output_image",
    "image_url": "data:image/png;base64,iVBORw0KGgo..."
  }
}

{
  "id": "resp_abc123",
  "object": "response",
  "status": "completed",
  "model": "gemini-3-pro-image-preview",
  "output": [
    {
      "id": "msg_abc123",
      "type": "message",
      "status": "completed",
      "role": "assistant",
      "content": [
        {
          "type": "output_text",
          "text": "Here's the image you requested:"
        },
        {
          "type": "output_image",
          "image_url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA..."
        }
      ]
    }
  ],
  "usage": {
    "input_tokens": 12,
    "output_tokens": 1024
  }
}

Supported Models

Model	Provider Route	Description
`gemini-3-pro-image-preview/google-ai-studio`	Google AI Studio	Nano Banana Pro - Google’s multimodal model with native image generation

Reasoning - Enable reasoning for complex tasks
Responses API - Alternative API format with image support

Getting Started

AI Gateway

Observability & Analytics

Prompt Management

Legacy Integrations

References

Quick Start

Configuration

image_generation

Handling Responses

Chat Completions

Responses API

Supported Models

​Quick Start

​Configuration

​image_generation

​Handling Responses

​Chat Completions

​Responses API

​Supported Models

​Related

Quick Start

Configuration

image_generation

Handling Responses

Chat Completions

Responses API

Supported Models

Related