Yep, for all users it’s using your Progression Level for the relevant power zone, and choosing an assortment of different workouts appropriate to that level and at your specified duration. The thing that’s tying all those workouts together is Difficulty Level, which isn’t yet publicly visible. Difficulty levels use a combination of different factors to quantify the real-world challenge of a workout, and are a way to compare the actual experience of workouts with differing interval structures, rest periods, and interval lengths.