What actually changes for a widget between releases
Three things move, and only three. The tint modes — how iOS recolours a widget on the Lock Screen or a dimmed desktop. The surfaces — Home Screen, Lock Screen, StandBy, and since iOS 26 the CarPlay dashboard. And the shapes each surface offers, which is why the CarPlay square is a genuine design constraint rather than a setting.
Everything else is the same WidgetKit contract it has been since iOS 14: a timeline of pre-rendered entries, a refresh budget you do not control, and a per-second live view only where the system grants one.
That is why this site talks about surfaces rather than versions. When iOS 27 arrives, the designs that work today keep working; anything genuinely new gets its own layout, and this page will say what it is instead of promising it in advance.