The platform crossed the milestone last night, and it happened about a month and a half after the 25 million mark. Bluesky still has a long way to go to pass Threads, though; Meta’s platform has more than 100 million daily active users.
[Media: https://bsky.app/profile/bsky.app/post/3lgu4lg6j2k2v]
The difference is that you can easily move to another Mastodon instance, and it’s designed so that when you do that your followers / followees come with you.
Except you can’t move your posts. Or, really, anything other than followers.