The search box at the bottom of HN still links to this subdomain which means that HN searches are currently broken. So, hopefully this is just a temporary glitch or oversight.
Edit: Wow. One of those occurrences where something has always been there and I just never really noticed.
https://news.ycombinator.com/item?id=7126301 ("Last Friday, we have released the new HN Search (http://hn.algolia.com)")
(Found by plugging "hn.algolia.com" into hn.algolia.com and bisecting by date).