That's a good question because Arc the language is distinct from HN the application (and both were released all those years ago).
At the language level, we've changed things but not super much. It's maybe 30% different.
At the application level there have been many changes and it's more like 80% different.
Very neat! It would be cool to see, I'm sure. Anarki hadn't changed too much, but there are some things for sure. Any especially cool features added or changed? Must be cool to work in a language you control.
It is extremely satisfying! I would enjoy having community feedback about it too, but so far publishing a new version has been too heavy a lift. Maybe one of these years.
https://news.ycombinator.com/item?id=11240350 has discussion of one change we made to Arc, though it's already 8 years old - the midpoint between today and the original release of Arc, I guess.
Really cool! How different is Arc running HN or your extension from Arc3.1, the last-released version?