Image Generation - Helicone OSS LLM Observability

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.

Info

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#

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 imagesconst 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 outputconst 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

{  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"`)

Note

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#

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 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

Quick Start#

Configuration#

image_generation#

Handling Responses#

Chat Completions#

Responses API#

Supported Models#

Related#