https://atproto.com/guides/self-hosting
Edit: After digging in a bit, I believe the thing most people would consider as “running an instance” would be an appview and/or relay. Both of which they claim are ready, I just haven’t seen any. I think that part of the disconnect is that in ActivityPub the roles of what AT Protocol calls PDS, Relay, and AppView are all handled by a single instance. A PDS stores canonical data, a Relay aggregates PDSes, and an AppView is a UI reading from a relay.
https://github.com/bluesky-social/pds?tab=readme-ov-file#what-is-the-current-status-of-federation
That lets you host your own data. You cannot host an instance. You must use the Bluesky app with your PDS.