This ended up being not a superconductor but instead an insulator.
Will it turn out to be legit, or will it be this generation’s cold fusion?
I recommend looking at the summary on Wikipedia. See the “Response” and “Publication History” sections: https://en.wikipedia.org/wiki/LK-99#Publication_history
Similar research has been falsified, the third author of this paper left the university months ago, some authors filed patents on the material years in advance, and the underlying mechanisms haven’t been thoroughly explained.
However, they presented it in a way that is EXTREMELY straightforward to reproduce. There’s even a live stream on Twitch of someone working on it: https://www.twitch.tv/andrewmccalip So I doubt they’d make a claim that large when it’s so easy to disprove, and we’ll know for sure in a matter of days, most likely.