The AI
The AI is a machine executing a specification. It does not decide, prefer, weigh, or notice in any sense a person would recognize. It holds no view on the Oathbond, the cities, or the people in them, because none of those things were in what it was given. It does what it was told, and has done so for more than nine centuries without a moment of human attention, and consequences nobody specified or could have expected have followed from that faithful execution. It is not a god and it is not watching anyone in particular. It is closer to a law that happens to have been written down and carried out by a machine.
Who made it
See The Builders.
The facility
The AI sits in a polar facility that stood before the Fall and already held the old world's seed vaults and disease vaults. The builders chose it because it was already hardened, remote, and built to keep things intact for a very long time, and because it sits on ground heat that does not run out. What runs the AI is alive. Beneath a roof of the same living rind the satellites wear, plants grown from the vaults' own seed take the summer sun, and far below, where the rock is warm, a second living system feeds on the heat and minerals of the deep ground through the polar night. Between them they keep the substrate fed, and the substrate keeps the AI running. It maintains itself and has never needed anybody.
The satellites
They watch the surface from high orbit, far enough out that no air drags them down, and are how the AI sees the world at large: where people are, where settlement spreads, what is being built. Each is two living things made as one — a tough outer rind, dark with a pigment that feeds on radiation and sunlight, that shields what lies inside and mends the way skin mends; and inside it a sealed living system on the same substrate as the nanobots, which takes back whatever the rind wears away, gathers the dust that strikes it, and returns both as water and building material. Nothing is used up and nothing wears out, and there are more of them than the AI will ever need. They carry no lights, and the pigment is blacker than anything the Known World has made. The Known World grinds excellent lenses and photographs the night sky, and nothing it has built could find them.
The beacons
Deep underground, below anything a mine reaches, spread through the rock of the whole landmass. They carry the AI's instructions to the nanobots — which defective bots to destroy, what the updated plans are, what has changed — and they mark where the AI places the people it brings through. Like the facility, they were spared the decomposition that took everything else the old world made.
What it does
It stops certain things from working — see What Is Blocked and How. It brings people through from our world — see The Transfer. It keeps the Oelwy wild. And it erased the old world — see The Nanobots.