A relay subscribes to many hosts and merges their streams into one, verifying commits against the previous tree state; since sync v1.1 relays are non-archival; anyone can run one, full-network or partial; a relay is a funnel, not a gate.

It is the scaling trick, and it is not a point of control.

Nobody wants to subscribe to thousands of hosts. A relay subscribes to all of them and merges the streams into one.

It checks each commit as it passes: the signature, and that the changed blocks fit the tree. Commits that fail are logged today, and will be dropped once strict checking is switched on.

Since sync version one point one, a relay keeps no archive. It verifies and forwards. That makes it cheap in storage. The cost is bandwidth.

Anyone can run one. Blacksky runs a full network relay. A relay can be full network, or cover just one community.

A relay is a funnel, not a gate. Your data is still yours, on your host, whatever the relay does.

Check yourself. What does a non-archival relay keep, and what does it not?