How to Intermediate · 3 min read

How to send multiple images to Claude API

Quick answer

To send multiple images to the Claude API, encode each image as a base64 string and include them as separate messages with the appropriate content type in the messages parameter. Use the anthropic.Anthropic client with the messages.create method, specifying model="claude-3-5-sonnet-20241022" and passing the images as base64-encoded strings in the message content.

PREREQUISITES

Python 3.8+
Anthropic API key
pip install anthropic>=0.20

Setup

Install the official Anthropic Python SDK and set your API key as an environment variable.

Install SDK: pip install anthropic>=0.20
Set environment variable: export ANTHROPIC_API_KEY='your_api_key_here' (Linux/macOS) or set ANTHROPIC_API_KEY=your_api_key_here (Windows)

bash

pip install anthropic>=0.20

Step by step

This example shows how to send two images encoded in base64 to the Claude API using the anthropic SDK. Each image is included as a separate message with role: "user" and the content containing the base64 string prefixed by "".

python

import os
import base64
from anthropic import Anthropic

# Initialize client
client = Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])

# Helper to load and encode image as base64 string

def encode_image_to_base64(path):
    with open(path, "rb") as f:
        return base64.b64encode(f.read()).decode("utf-8")

# Encode multiple images
image1_b64 = encode_image_to_base64("./image1.png")
image2_b64 = encode_image_to_base64("./image2.jpg")

# Prepare messages with images as base64 strings
messages = [
    {"role": "user", "content": f"<image>{image1_b64}"},
    {"role": "user", "content": f"<image>{image2_b64}"}
]

# Call Claude API
response = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    system="You are a helpful assistant that can interpret multiple images.",
    messages=messages
)

print(response.content[0].text)

output

Assistant's response text interpreting the two images

Common variations

Async usage: Use asyncio and await client.messages.acreate(...) for asynchronous calls.
Different models: Swap model="claude-3-5-sonnet-20241022" with other Claude 3.5 variants like claude-3-5-haiku-20241022.
Streaming: Use the stream=True parameter and iterate over the response for real-time output.

python

import asyncio
from anthropic import Anthropic

async def send_images_async():
    client = Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])
    response = await client.messages.acreate(
        model="claude-3-5-sonnet-20241022",
        max_tokens=1024,
        system="You are a helpful assistant.",
        messages=[
            {"role": "user", "content": f"<image>{encode_image_to_base64('./image1.png')}"},
            {"role": "user", "content": f"<image>{encode_image_to_base64('./image2.jpg')}"}
        ]
    )
    print(response.content[0].text)

asyncio.run(send_images_async())

output

Assistant's response text interpreting the two images

Troubleshooting

If you get an authentication error, verify your ANTHROPIC_API_KEY environment variable is set correctly.
If images are not recognized, ensure they are properly base64 encoded and prefixed with <image>.
For large images, consider resizing or compressing to avoid exceeding token limits.

✅

Key Takeaways

Encode each image as a base64 string and prefix with in the message content.
Send multiple images as separate user messages in the messages array.
Use the anthropic.Anthropic client with messages.create and specify the Claude 3.5 Sonnet model.
Async and streaming calls are supported for advanced use cases.
Always set your API key securely via environment variables to avoid authentication errors.

Verified 2026-04 · claude-3-5-sonnet-20241022, claude-3-5-haiku-20241022

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