Gemini Image Generation Migration Guide

Who is impacted by this change?

Anyone using the following models with /chat/completions:

• gemini/gemini-2.0-flash-exp-image-generation
• vertex_ai/gemini-2.0-flash-exp-image-generation

Key Change

Gemini models now support image generation through chat completions. Images are returned in response.choices[0].message.image with base64 data URLs.

Before and After

Before

from litellm import completion

response = completion(
    model="gemini/gemini-2.0-flash-exp-image-generation",
    messages=[{"role": "user", "content": "Generate an image of a cat"}],
    modalities=["image", "text"],
)


base_64_image_data = response.choices[0].message.content

After

from litellm import completion

response = completion(
    model="gemini/gemini-2.0-flash-exp-image-generation",
    messages=[{"role": "user", "content": "Generate an image of a cat"}],
    modalities=["image", "text"],
)

# Image is now available in the response
image_url = response.choices[0].message.image["url"]  # "data:image/png;base64,..."

Why the change?

Because the newer gemini-2.5-flash-image-preview model sends both text and image responses in the same response. This interface allows a developer to explicitly access the image or text components of the response. Before a developer would have needed to search through the message content to find the image generated by the model.

Usage

Using the Python SDK

Key Change:

# Before
-- base_64_image_data = response.choices[0].message.content

# After
++ image_url = response.choices[0].message.image["url"]

Basic Image Generation

from litellm import completion
import os

# Set your API key
os.environ["GEMINI_API_KEY"] = "your-api-key"

# Generate an image
response = completion(
    model="gemini/gemini-2.0-flash-exp-image-generation",
    messages=[{"role": "user", "content": "Generate an image of a cat"}],
    modalities=["image", "text"],
)

# Access the generated image
print(response.choices[0].message.content)  # Text response (if any)
print(response.choices[0].message.image)    # Image data

Response Format

The image is returned in the message.image field:

{
    "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...",
    "detail": "auto"
}

Using the LiteLLM Proxy Server

Key Change:

# Before
-- "content": "base64-image-data..."

# After  
++ "image": {
++   "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...",
++   "detail": "auto"
++ }

Configuration Setup

1. Configure your models in config.yaml:

model_list:
  - model_name: gemini-image-gen
    litellm_params:
      model: gemini/gemini-2.0-flash-exp-image-generation
      api_key: os.environ/GEMINI_API_KEY
  - model_name: vertex-image-gen  
    litellm_params:
      model: vertex_ai/gemini-2.5-flash-image-preview
      vertex_project: your-project-id
      vertex_location: us-central1

general_settings:
  master_key: sk-1234  # Your proxy API key

2. Start the proxy server:

litellm --config /path/to/config.yaml

# RUNNING on http://0.0.0.0:4000

Making Requests

Using OpenAI SDK:

from openai import OpenAI

# Point to your proxy server
client = OpenAI(
    api_key="sk-1234",  # Your proxy API key
    base_url="http://0.0.0.0:4000"
)

response = client.chat.completions.create(
    model="gemini-image-gen",
    messages=[{"role": "user", "content": "Generate an image of a cat"}],
    extra_body={"modalities": ["image", "text"]}
)

# Access the generated image
print(response.choices[0].message.content)  # Text response (if any)
print(response.choices[0].message.image)    # Image data

Using curl:

curl -X POST 'http://0.0.0.0:4000/v1/chat/completions' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer sk-1234' \
-d '{
  "model": "gemini-image-gen",
  "messages": [
    {
      "role": "user",
      "content": "Generate an image of a cat"
    }
  ],
  "modalities": ["image", "text"]
}'

Response format from proxy:

{
  "id": "chatcmpl-123",
  "object": "chat.completion",
  "created": 1704089632,
  "model": "gemini-image-gen",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "Here's an image of a cat for you!",
        "image": {
          "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...",
          "detail": "auto"
        }
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 10,
    "completion_tokens": 8,
    "total_tokens": 18
  }
}