- Auto-default anthropic-version to 2023-06-01 for prompt caching
- Forward cache headers (x-cache, cf-cache-status, age, etc.) from backend
- Add features: ["prompt_caching"] to /v1/models response
- Extract and report actual usage tokens in streaming message_delta
- Track output char count for token estimation when backend omits it
- Cache-aware usage reporting: cache_creation_input_tokens, cache_read_input_tokens
- Comprehensive tests for cache_control preservation in content blocks & system
- Add anthropicPassthrough flag to BackendConfig for native Anthropic backends
- Preserve cache_control on content blocks and system prompt (keep structured)
- Extract and forward anthropic-version header from client to backend
- Report actual token usage from backend response (input_tokens, output_tokens)
- Support native Anthropic passthrough (no translation) for compatible backends
- Wire anthropic-version through all entry points: index.ts, router.ts, worker.ts