Classes aren't the traditional ones you find in other games. Those defines all of your abilities and what you can and cannot do. Alteratio doesn't restrict you to follow along a certain path - everything can be changes. So instead of cycling through multiple classes, you evolve overall and eventually reach what would be defined as a 'class'. If you know how to pick locks, sneak by people, and disarm traps, you would unlock the 'Rogue' class.
After getting access to a class, you get a small toggleable 'perk' to enhance that playstyle. You'll gain a few special abilities pertaining to that class, including but not limited to: interactions with others, combat abilities, roleplay effects that will come up eventually, and access to special gear.
There are a plethora of classes to be unlocked in a variety of ways. Many are along a single path of generally improving your skill, some are hybrid versions between two or more classes, and some are from special events or from your actions in the world!
You can have 2 classes at anytime and switch between them as you see fit apart from in the middle of an interaction since becoming something beneficial to a situation that you did not know about is the opposite of what Alteratio is - you need to be expecting the unexpected!
As soon as I start more development on Classes, I'll begin writing down all the classes here!