PRODUCTION SCENARIO
A claims triage bot sends an 8,000-token policy manual as static system content, followed by one final block holding a timestamp and the claimant's message. The team put cache_control on that final block and sees zero cache reads across 5,000 requests a day.
Where should the cache breakpoint go?
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Show answer and explanation
Answer: On the last block of the static policy manual, before the timestamp
A breakpoint writes one entry, a hash of the prefix ending at that block, and later requests look backward for prior writes rather than for stable content, so the breakpoint belongs at the end of the static prefix. The one-hour TTL keeps alive an entry whose hash still never matches. A timestamp-only block still changes every request, so its hash changes too. Removing every breakpoint writes nothing, because the API does not hunt for the longest common prefix on its own.