Why your agent bills spike mid-task: the prefix cache, explained with numbers
This story is from 2026-09-20. It is preserved in the archive; the latest stories are on the live feed.
Multi-agent runs bill in a weird shape: most requests are cheap, then one request costs 10x its neighbors. I hit this enough times that I started logging the JSONL usage objects, and the pattern turned out to be prompt-cache invalidation. This post explains the mechanism with the numbers from my ow…
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- 2026-09-20 06:40 · DEV Community — AI
Why your agent bills spike mid-task: the prefix cache, explained with numbers