Quiz or challenge shared on HN. User allowed to take test only once, or rather something about the test made subsequent attempts not valid. (You learn something about the test as you take it.) At the end you receive a percentile score relative to other users. I don't exactly remember the content or what was being tested. Possibly it had something to do with LLMs.
I believe I found it: <a href="https://nicholas.carlini.com/writing/llm-forecast/question/Capital-of-Paris" rel="nofollow">https://nicholas.carlini.com/writing/llm-forecast/question/C...</a>