Pro isn't unlimited in the way the old plan felt. Roughly: your plan includes a fixed amount of model usage priced at API rates, and once that's gone Cursor bills extra usage if on-demand spending is enabled. Picking a frontier model with Max mode on a big codebase eats that allowance fast, because every request sends a lot of context.
See where it went: cursor.com > Dashboard > Usage. It lists each request with model, tokens and cost. You'll probably see a handful of requests at $1-3 each.
Make it stop at $20: Dashboard > Settings / Spending: set the on-demand limit to $0 (or disable it). Then you just get throttled or pushed to the cheaper option instead of billed.
Spend less:
- Use Auto or a cheaper model for everyday edits, switch to the big model only for hard problems.
- Turn Max mode off unless you really need the huge context.
- Start a new chat per task. Long chats resend the whole history every message.
- Don't @ the whole codebase, @ the 2-3 files that matter.