A team includes a per-request timestamp in the cached system prompt prefix. What is the consequence?
Answer: Invalidates the cache on every call — every call becomes a cache write at ~125% of input price
The cache key is the literal bytes of the prompt prefix. A per-request timestamp guarantees every cache key is unique, meaning every call writes a new cache entry (~125% input price) with zero hits. Move dynamic content (timestamps, request IDs) below the cache breakpoint.