Anthropic Python SDK

Common errors

• ModuleNotFoundError: No module named 'anthropic'

  cause The 'anthropic' package is not installed in the Python environment.
  fix Install the package using 'pip install anthropic'.

• ImportError: cannot import name 'Anthropic' from 'anthropic'

  cause The import statement is incorrect; 'Anthropic' is not a valid import from the 'anthropic' package.
  fix Use 'from anthropic import AnthropicClient' instead.

• AttributeError: module 'anthropic' has no attribute 'Anthropic'

  cause The 'Anthropic' class does not exist in the 'anthropic' module.
  fix Instantiate the client with 'client = anthropic.AnthropicClient()'.

• TypeError: __init__() missing 1 required positional argument: 'api_key'

  cause The 'AnthropicClient' class requires an 'api_key' argument during initialization.
  fix Initialize with 'client = anthropic.AnthropicClient(api_key="your_api_key")'.

• ValueError: Invalid API key provided

  cause The provided API key is incorrect or malformed.
  fix Ensure the API key is correct and properly formatted.

Warnings

• breaking anthropic.Client() is removed. Use anthropic.Anthropic() instead.
  Fix: client = Anthropic(api_key=os.environ.get('ANTHROPIC_API_KEY'))
• gotcha SDK releases weekly. Pin your version in production or expect frequent behaviour changes.
  Fix: Pin with anthropic==0.84.0 in requirements.txt
• gotcha message.content is a list, not a string. Access text via message.content[0].text.
  Fix: print(message.content[0].text) not print(message.content)
• gotcha max_tokens is required. No default value. Omitting raises a validation error.
  Fix: Always pass max_tokens=1024 or appropriate value
• deprecated claude-agent-sdk-python no longer requires Claude Code to be installed separately. It is bundled.
  Fix: Remove any separate Claude Code install steps from your setup.
• breaking The package `claude-agent-sdk` is not a valid PyPI package and cannot be found. If you are trying to install the main Anthropic SDK, use `anthropic`. If you are looking for an agent-specific SDK, you might be looking for `claude-agent-sdk-python`.
  Fix: Replace `claude-agent-sdk` with `anthropic` or `claude-agent-sdk-python` in your requirements/install commands.
• breaking Failed to authenticate due to missing API key. Ensure `api_key` is passed during client initialization or set the `ANTHROPIC_API_KEY` environment variable.
  Fix: client = Anthropic(api_key=os.environ.get('ANTHROPIC_API_KEY'))

Install

• pip install anthropic Python (core SDK)
• pip install claude-agent-sdk Python (agent SDK)
• npm install @anthropic-ai/sdk Node.js

Imports

• Anthropic
  wrong:

  import anthropic; anthropic.Client(api_key=...)

  correct:

  from anthropic import Anthropic

  anthropic.Client is the old pre-0.3 API. Removed. Always use Anthropic() class.
• AsyncAnthropic
  wrong:

  import anthropic; anthropic.AsyncClient()

  correct:

  from anthropic import AsyncAnthropic

  Use AsyncAnthropic for async contexts, not the legacy async client.

Quickstart

Minimal message call using the Anthropic SDK 0.84.x.

from anthropic import Anthropic

client = Anthropic()  # reads ANTHROPIC_API_KEY from env
message = client.messages.create(
    model='claude-opus-4-6',
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude"}
    ]
)
print(message.content[0].text)