Question 1139

Zero Percent Hit Rate

Your assistant sends a 9,000 token system prompt of tool definitions and policy text, prefixed with a line reading "Current time: 2026-08-15T14:03:21Z". Prompt caching is enabled with a breakpoint at the end of that block, but the cache hit rate is essentially zero. What is the fix?

A

Pad the block, since it currently falls under the provider's minimum cacheable length

B

Move the timestamp below the stable block so the cached prefix is identical across requests

C

Extend the cache lifetime to the longer TTL tier so entries survive between requests

D

Add more cache breakpoints inside the tool definitions to increase match granularity