Anthropic Known Pitfalls Overview Ten common mistakes when building with the Anthropic API and how to avoid them: forgetting (required), system prompt in messages array (wrong), non-alternating messages, unchecked , creating client per request, no 529 handling, hardcoded model IDs, expensive output tokens, no streaming, and unnecessary PII. 1. Forgetting Unlike OpenAI, is required . Omitting it returns a 400 error. 2. System Prompt in Messages Array Claude uses a top-level parameter, not a system message in the array. 3. Non-Alternating Messages Messages must strictly alternate between user a…