Build with Claude Messages API using structured outputs for guaranteed JSON schema validation.

• Structured outputs (v0.69.0+) guarantee JSON format compliance with two modes: JSON outputs for data extraction and strict tool use for validated function parameters; always validate semantic correctness as models can still hallucinate
• Supports prompt caching with up to 90% cost savings; cache_control must be placed on the LAST block, with 1,024+ token minimum for Sonnet and 2,048+ for Haiku
• Covers streaming SSE, tool use with error handling, vision image processing (JPEG/PNG/WebP/GIF, max 5MB), and rate limit retry logic with retry-after header respect
• Prevents 16 documented errors including MCP 2-minute timeout issues, U+2028 Unicode sanitization in tool results, streaming error handling (fixed in v0.71.2), and structured output hallucination risks
• Active models: Claude Opus 4.5, Claude Sonnet 4.5, Claude Haiku 4.5, Claude Opus 4; Claude 3.5/3.7 Sonnet retired as of Oct 2025