I was closing in on his Nexus with an army consisting mostly of Artemis and Apollo cruisers. The units that the AI usually has at home started to come out--then went back--and out and back. This kept up until they were dead--they never got close enough to fire a shot.
It's possible this was a visibility issue somehow as aircraft were also showing up and getting blown out of the sky, but if so the timing was surprising. I was within one of his regions but all the buildings there were destroyed and I don't think he could see me from there. I do not know if he had radar or not as his buildings were dying generally beyond my visibility range.