The Nanobots
The nanobots are the AI's hands, and the only part of it anyone in the world has ever touched. They are an organic computing substrate at the scale of a virus — between a hundred-thousandth and a ten-thousandth of a Threid — and the microscopes of the Known World, which resolve a bacterium comfortably, cannot resolve anything this small. They are in the soil, the water, and the air of every city and every stretch of Frontier, and nobody has ever seen one.
They replicate themselves, and the beacons keep them to their purpose: a bot that has drifted from its plan is culled, and the whole population is updated when the plan changes. What they work on is the world, never people. They alter what a material does, what a reaction produces, and what a signal does along a wire. They do not reach into a body.
Erasure
Their first work was erasure. Through the Great Arrival and the century after, the nanobots broke down the garbage of the old world and every piece of its technology so that nothing would be left to study or copy. Organic waste went first; metal corroded past recognition; the plastics that would have outlasted everything were taken apart and returned to the soil. Nothing the old world manufactured survives. What it left behind that is still here is alive, and was never on the list — see What the Old World Left Behind.