Ehhh, I'd say Bluesky isn't really built on this fediverse (which uses ActivityPub) but is wanting to make its own fediverse for its own needs (using their own protocol). Part of their reasoning was because of ActivityPub's issues with account portability. Whether Bluesky will be successful or not in their goals is another matter, though - I've heard somewhere ActivityPub is getting proper account portability in the future, but with no time-frame.

But it's still nice to have options. I use both fediverse and Bluesky and I like fedi more in a technical sense (emoji reacts, text formatting, overall a matured platform) but Bluesky more culturally (a lot looser, not so much "social media for Linux users").

Bluesky is building their own thing, called the Authenticated Transfer Protocol, or atproto for short.

Federation is planned, but there are still behaviors of atproto that are as of yet undefined, and need to be defined and ironed out before Bluesky's primary network is open to federation.

Well its probably dead anyways. Dorsey already left it and moved to Noster.