Why My LLM Feature Cost More Than It Should: Field Notes on Prompt Caching, Cache Breakpoints, and the Timestamp That Killed Every Hit
This story is from 2026-10-07. It is preserved in the archive; the latest stories are on the live feed.
Headline: Prompt caching saves money only when the cached prefix is byte-identical across requests, and a single interpolated timestamp in a system prompt is enough to make every call a cache write instead of a cache read. The three things that fixed my bill were ordering the request static-first (…
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- 2026-10-07 06:00 · DEV Community — AI
Why My LLM Feature Cost More Than It Should: Field Notes on Prompt Caching, Cache Breakpoints, and the Timestamp That Killed Every Hit