Comment by tialaramex

The clocks we have all basically work in TAI. Historically UTC is TAI plus occasionally a bodge (the leap second) to move it closer to UT1 when it's wrong by too much.

Nobody has a real UT1 clock†, some observation sites prepare guesses at UT1 mostly in terms of how far it deviates from TAI because you can just buy clocks that keep TAI really well.

† You could say this damp rock, "The Earth" is such a clock, and I guess I reluctantly accept that argument but then OK the UI for that clock is abysmal, nobody can use this the way you'd use an actual clock unless they accept miserably bad precision.