Crawford says it’s the biggest yet, with 7 classes (Experts: Ranger, Rogue, Bard; Priests: Cleric, Paladin, and Druid; and Monk confirmed), spells and weapon mastery tweaks, capstones back at lvl20 (epic boons will be pushed to another UA), and subclass progression reverted to the 2014 cadence after lvl3. Notably, rogues are seemingly getting another feature at lvl5 to make up for the fact that they get very nothing from their subclass between 3 and 9.
Oh for sure that’s why they’re doing it. Subclasses require a bucket of features when you first get them in order to substantially differentiate themselves from the main class, which means it’s a big power jump. All the most common dips in 5e (warlock, cleric, sorcerer) are classes that get their subclass at 1st level.