Anthropic API Client AI Skill Guide (Claude)

Overview & Engine Architecture

The Anthropic SDK talks to the Messages API (messages.create / stream). Requests require model and max_tokens; optional system, alternating user/assistant turns, tools, and cache_control breakpoints. Tool use returns tool_use content blocks; the client must execute allowlisted tools and continue with tool_result. Prompt caching prefixes follow tools → system → messages. Pin current model ids (verify deprecations); never invent keys.