The BGS (which is an atproto "relay" service) subscribes to all PDS event streams on the entire network, and aggregates and relays them. This way it's possible

The BGS (which is an atproto "relay" service) subscribes to all PDS event streams on the entire network, and aggregates and relays them. This way it's possible to get all network data from a single place (the BGS) rather than having to connect to every PDS, which is simpler for consumers and dramatically reduces the workload of PDS hosts. Some details about event streams here, although the APIs are still evolving: https://atproto.com/specs/event-stream https://atproto.com/specs/event-stream