Image Generation in Chat Completions, Responses API

This guide covers how to generate images when using the chat/completions. Note - if you want this on Responses API please file a Feature Request here.

info

Requires LiteLLM v1.76.1+

Supported Providers:

• Google AI Studio (gemini)
• Vertex AI (vertex_ai/)

LiteLLM will standardize the image response in the assistant message for models that support image generation during chat completions.

Example response from litellm

"message": {
    ...
    "content": "Here's the image you requested:",
    "image": {
        "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...",
        "detail": "auto"
    }
}

Quick Start

SDK

Image generation with chat completion

from litellm import completion
import os 

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

response = completion(
    model="gemini/gemini-2.5-flash-image-preview",
    messages=[
        {"role": "user", "content": "Generate an image of a banana wearing a costume that says LiteLLM"}
    ],
)

print(response.choices[0].message.content)  # Text response
print(response.choices[0].message.image)    # Image data

PROXY

1. Setup config.yaml

config.yaml

model_list:
  - model_name: gemini-image-gen
    litellm_params:
      model: gemini/gemini-2.5-flash-image-preview
      api_key: os.environ/GEMINI_API_KEY

2. Run proxy server

Start the proxy

litellm --config config.yaml

# RUNNING on http://0.0.0.0:4000

3. Test it!

Make request

curl http://0.0.0.0:4000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $LITELLM_KEY" \
  -d '{
    "model": "gemini-image-gen",
    "messages": [
      {
        "role": "user",
        "content": "Generate an image of a banana wearing a costume that says LiteLLM"
      }
    ]
  }'

Expected Response

{
    "id": "chatcmpl-3b66124d79a708e10c603496b363574c",
    "choices": [
        {
            "finish_reason": "stop",
            "index": 0,
            "message": {
                "content": "Here's the image you requested:",
                "role": "assistant",
                "image": {
                    "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...",
                    "detail": "auto"
                }
            }
        }
    ],
    "created": 1723323084,
    "model": "gemini/gemini-2.5-flash-image-preview",
    "object": "chat.completion",
    "usage": {
        "completion_tokens": 12,
        "prompt_tokens": 16,
        "total_tokens": 28
    }
}

Streaming Support

SDK

Streaming image generation

from litellm import completion
import os 

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

response = completion(
    model="gemini/gemini-2.5-flash-image-preview",
    messages=[
        {"role": "user", "content": "Generate an image of a banana wearing a costume that says LiteLLM"}
    ],
    stream=True,
)

for chunk in response:
    if hasattr(chunk.choices[0].delta, "image") and chunk.choices[0].delta.image is not None:
        print("Generated image:", chunk.choices[0].delta.image["url"])
        break

PROXY

Streaming request

curl http://0.0.0.0:4000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $LITELLM_KEY" \
  -d '{
    "model": "gemini-image-gen",
    "messages": [
      {
        "role": "user",
        "content": "Generate an image of a banana wearing a costume that says LiteLLM"
      }
    ],
    "stream": true
  }'

Expected Streaming Response

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1723323084,"model":"gemini/gemini-2.5-flash-image-preview","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1723323084,"model":"gemini/gemini-2.5-flash-image-preview","choices":[{"index":0,"delta":{"content":"Here's the image you requested:"},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1723323084,"model":"gemini/gemini-2.5-flash-image-preview","choices":[{"index":0,"delta":{"image":{"url":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA...","detail":"auto"}},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1723323084,"model":"gemini/gemini-2.5-flash-image-preview","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

Async Support

Async image generation

from litellm import acompletion
import asyncio
import os 

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

async def generate_image():
    response = await acompletion(
        model="gemini/gemini-2.5-flash-image-preview",
        messages=[
            {"role": "user", "content": "Generate an image of a banana wearing a costume that says LiteLLM"}
        ],
    )
    
    print(response.choices[0].message.content)  # Text response
    print(response.choices[0].message.image)    # Image data
    
    return response

# Run the async function
asyncio.run(generate_image())

Supported Models

Provider	Model
Google AI Studio	gemini/gemini-2.5-flash-image-preview
Vertex AI	vertex_ai/gemini-2.5-flash-image-preview

Spec

The image field in the response follows this structure:

"image": {
    "url": "data:image/png;base64,<base64_encoded_image>",
    "detail": "auto"
}

• url - str: Base64 encoded image data in data URI format
• detail - str: Image detail level (always "auto" for generated images)

The image is returned as a base64-encoded data URI that can be directly used in HTML <img> tags or saved to a file.