bummer. i used to like the legend that it was all on one commodity linux pc implemented in some nice concise lisp running on sbcl.
edit: my memory is crap. it was a single machine, but the codebase was written in a custom experimental language that i think was a lisp derivative. (which would make sense!). the source was online at some time, can't find it now.
I understand the backend is still somewhat limited. After Altman was fired (IIRC) when HN got 1000s of comments within no time, dang asked everyone to logout and login again, to make life for the poor machine a bit easier. So besides limited HW resources, also some non-optimal implementation details ;)
It still is a single single-core server, dang references it frequently when there's unusually high traffic [0]. And the language you're referring to is Arc [1]. They do have caching for not-logged-in users, historically done through nginx [2]. From other comments in this thread, it sounds like they just temporarily put Cloudflare in front of that single server to block a DDoS.
edit: my memory is crap. it was a single machine, but the codebase was written in a custom experimental language that i think was a lisp derivative. (which would make sense!). the source was online at some time, can't find it now.