Setup & your first request

Before you can build anything with Claude, you need an API key and a working Python (or TypeScript) environment. Install the official SDK, export your key as an environment variable, and make your first call to the Messages API.

import anthropic

client = anthropic.Anthropic()  # reads ANTHROPIC_API_KEY from the environment

message = client.messages.create(
    model="claude-sonnet-5",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude! What can you help me with?"}
    ],
)

print(message.content[0].text)

Key takeaways: the API key should always come from an environment variable or secret store, never hardcoded in source or committed to git. The Messages API is stateless — each request is independent, so a multi-turn conversation means resending the full message history every time. Finally, max_tokens caps the length of the response, not a fixed cost — set it high enough for what you expect to receive.