Fundamentally there isn't any change in the underlying physics. You're limited by the half life of the isotope, so you either choose a longer-lived isotope (which actually may be even harder post Cold War as much of the ideal isotopes were byproducts of nuclear weapons manufacturing) or launch a bigger RTG than you need so you have enough power later on in the mission.

yep i think the newer ones use a different fuel that is longer lived, and advances in tech around it make it more viable than it was decades ago

wiki has the answer, ballpark is around twice as long, and they're using this new design for an upcoming probe

I think the more interesting thing is its suddenly become so much cheaper to put things in orbit, we could simply put a larger satellite with a larger nuclear battery out there.