Anthropic Python SDK

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.
• gotcha Model IDs are frequently hallucinated by LLMs. Observed wrong values: claude-opus-4-20250514, claude-3-opus-20240229, claude-opus-4-0. Wrong model ID gives a 404 at runtime with no helpful error message.
  Fix: Always verify model IDs at https://docs.anthropic.com/en/docs/about-claude/models — copy the exact string from the docs. Do not guess or interpolate.

Install

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

Imports

• Anthropic

  from anthropic import Anthropic

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

  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)