#Cache

Your prototype cost R$ 12 on day one. In production, with 200 users, it costs almost R$ 4,000 a month. We open up the token bill of a real agent layer by layer (system prompt, tool definitions, RAG chunks, history, tool results) and show where almost 80% of the money disappears. In the end, prompt compression, history pruning, and context selection cut the bill by 73%, with the before-and-after spreadsheet.

You send a one-line question and /usage reports a whole day's worth of consumption. Saving tokens in a coding assistant has nothing to do with prompt size: it's about prefix caching. How it works in Claude Code, Codex, and Cursor, the seven actions that invalidate it without you noticing, how to measure it with cache_read vs cache_creation, and eight levers to stretch the session.