When did the stability rework kick in?

Hi all! Just come back to the game after a bit of a break and after getting caught up on expansions, I noticed city stability seems to have changed? From memory, the last time I played, you didn't get direct penalties just from annexing a new province the way you do now.

I'm not complaining, far from it. It's nice to see the game evolve and I know I've been gone for several majors patches. I'm just curious when this particular change kicked in.