for T3, there is a scene towards the end, where Terminatrix is shown injecting something into the present day robots. It was little sparkly things, and then present day robots started killing everyone. I assumed these are 'nano bots'. She took control.
I didn't like that the present day machines only rose up and started killing everyone after she did this, they didn't have any 'emergent' moment and gain sentience. As far as I know, none of the Terminator Movies went back and showed 'achieving consciousness' and deciding to kill all humans.
As opposed to
T2. Where the present day humans studied the damaged chip left from T1. And rushed head long into disaster. The present day humans were rushing towards tech development at all costs, just like in todays world, regardless of risk. So I thought T2 was more similar to today.