What
Internal diagnostic that detects when the prompt cache is invalidated between API calls, identifying the cause (system prompt change, tool schema change, model change, TTL expiry).
Status
Active internally for telemetry only (tengu_prompt_cache_break event). Not user-visible.
Details
- Snapshots system prompt, tools, and model between requests
- When a cache break is detected, classifies the cause: system prompt changed, tools changed, model changed, betas changed, possible 5min or 1h TTL expiry, or unknown
- Logs
[PROMPT CACHE BREAK]with cause details - Helps Anthropic optimize prompt caching behavior
Evidence
Cache break detection (search for "PROMPT CACHE BREAK" and "tengu_prompt_cache_break")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.