> One of the core primitives of the AT Protocol that underlies Bluesky is the firehose. It is an authenticated stream of events used to efficiently sync user updates (posts, likes, follows, handle changes, etc). Many applications people will want to build on top of atproto and Bluesky will start with the firehose, from feed generators to labelers, to bots and search engines. In the atproto ecosystem, there are many different endpoints that serve firehose APIs. Each PDS serves a stream of all of the activity on the repos it is responsible for. From there, relays aggregate the streams of any PDS who requests it into a single unified stream. This makes the job of downstream consumers much easier, as you can get all the data from a single location. https://docs.bsky.app/docs/advanced-guides/firehose