How coding agents like Cursor quietly cut input costs by reusing KV states across turns — and what actually breaks the cache

Why my Cursor bill looked weird

I was poking around my usage dashboard in Cursor and noticed a metric I'd never paid attention to before: Cache Read.

Date Type Model Tokens

May 2, 06:50 PM Included auto 898K → Cache Read

May 2, 06:49 PM Included auto 1.4M → Cache Write