Why I've paid 55k tokens on some cache read on new chat

Support Help
1

What is in that cache. I’ve reopened Cursor after not using it a while ( after trial expired ) bought the Pro+ subscription opened a single file and asked:

Change ToggleSwitch from horizontal to vertical and make the knob more square with rounded corners. Also please print out the scope/context you have used at the end.

it correctly did the job and at the end printed:

Scope/context used
File: pkg/ui/toggle.go (full file read).
Scope: Only this file was edited; no other packages or call sites were opened.
APIs: Fyne v2 (fyne.io/fyne/v2, canvas.Rectangle, fyne.Size, fyne.NewPos, fyne.NewSize), existing ToggleSwitch and toggleRenderer types.
Behavior: Toggle remains off = bottom, on = top; tap still toggles and calls OnChanged; colors and SetChecked unchanged.
No: Other UI files (e.g. reminder-list.go), tests, or assets were read or modified.

And in usage page this little prompt generated almost 79k tokens 55k of which is some cache read!?

3

The cache read tokens are coming from Cursor loading the Fyne v2 library context into its prompt. Cursor likely has a system prompt or tool-use block that loads relevant Go package documentation or type stubs for the libraries it detects in your file.

Fyne is a fairly large GUI framework. Cursor had already paid to build that Fyne/system-prompt context in a previous request (or during initialization), and you only got charged for the cache read rate, which is typically ~10% of the full input token cost. Without caching, that single prompt could have cost 5–10x more.

1 Like