alt Hacker NewsI took a quick look at the source:
// Fire view events (e.g. unlock_prompt_viewed) for any monetization prompt
// present in the freshly loaded page. data-analytics-view-events is a JSON
// array so one rendered prompt can report several events at once.
It's referring to the fact that after you complete 25 puzzles of a specific difficulty, it'll prompt you to unlock all the puzzles for a couple bucks. Helps offset server costs to run the site. So the comment in the code is addressing if a user has viewed that prompt or not. So not a "prompt" in the LLM sense.