Technically GPS cannot track TAI because TAI is not available in real time. You can compute TAI from UTC, but as mentioned above UTC is only created many days a

Technically GPS cannot track TAI because TAI is not available in real time. You can compute TAI from UTC, but as mentioned above UTC is only created many days after the fact. So in practice, you have to rely on what national labs provide. They provide time that is close to UTC but is not actually UTC, in the case of GPS they use the approximation of UTC by the US Naval Laboratories. Now because UTC is the official civil time, and it is easy enough to compute TAI from UTC, what such labs provide is UTC. Then internally, GPS translates that to GPS time. Which differs from TAI by 19 seconds.