How to beginner · 3 min read

How to set Anthropic API key as environment variable

Quick answer

Set your Anthropic API key as an environment variable using export ANTHROPIC_API_KEY='your_api_key' on Unix/macOS or setx ANTHROPIC_API_KEY "your_api_key" on Windows. In Python, access it securely with os.environ["ANTHROPIC_API_KEY"] when initializing the anthropic.Anthropic client.

PREREQUISITES

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

Setup environment variable

To keep your Anthropic API key secure, set it as an environment variable instead of hardcoding it in your code. This method works across operating systems.

Unix/macOS: Use the terminal command export ANTHROPIC_API_KEY='your_api_key'.
Windows (Command Prompt): Use setx ANTHROPIC_API_KEY "your_api_key" and restart your terminal.

Replace your_api_key with your actual Anthropic API key.

bash

export ANTHROPIC_API_KEY='sk-xxxxxx'

# Windows CMD:
setx ANTHROPIC_API_KEY "sk-xxxxxx"

Step by step usage in Python

After setting the environment variable, use the Anthropic SDK in Python to access it securely and create a client instance.

python

import os
import anthropic

# Initialize client with API key from environment variable
client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])

# Example: simple completion request
response = client.messages.create(
    model="claude-3-5-haiku-20241022",
    max_tokens=100,
    system="You are a helpful assistant.",
    messages=[{"role": "user", "content": "Hello Anthropic!"}]
)

print(response.content[0].text)

output

Hello Anthropic! How can I assist you today?

Common variations

You can set environment variables temporarily in your Python script for testing (not recommended for production):

python

import os
os.environ["ANTHROPIC_API_KEY"] = "sk-xxxxxx"  # For testing only

import anthropic
client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])

# Use client as usual

Troubleshooting

If you get a KeyError for ANTHROPIC_API_KEY, ensure the environment variable is set and your terminal or IDE was restarted after setting it.
Verify your API key is correct and has not expired.
On Windows, use PowerShell or Command Prompt accordingly and restart the shell after setx.

✅

Key Takeaways

Always set your Anthropic API key as an environment variable to keep it secure.
Access the API key in Python using os.environ["ANTHROPIC_API_KEY"] when creating the Anthropic client.
Restart your terminal or IDE after setting environment variables to ensure they are recognized.

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

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