I'd say not that well. It's still very young, and this is almost certainly a lot more users than the developers were originally expecting at this point in time.

Part of the motivation for them moving away from web sockets in the first place is because the bugs and inefficiencies with using websockets made it less efficient, increasing the amount of load when the instances got big.

Mass moderation and post sorting tools don't exist yet, and there's no automated moderation system, which is a must-have for big subreddits/communities.