Claude API

How do you authenticate with the Claude API?

Last verified: July 2026 · 2 min read
QUICK ANSWER

Authenticate with the Claude API by passing your API key in the 'x-api-key' request header. Specify the SDK version header 'anthropic-version' to ensure compatibility.

Direct Curl Request Authentication

curl https://api.anthropic.com/v1/messages   -H "x-api-key: your-api-key-here"   -H "anthropic-version: 2023-06-01"   -H "content-type: application/json"   -d '{
    "model": "claude-3-5-sonnet-20241022",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Hello!"}]
  }'
Verified against: Anthropic API v1

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