There will be a public alpha soon (this month, fingers crossed), so it won’t be too long until you’ve got something you can try.
Auto save in this case refers to periodically saving the current session, so in the event of a crash or power loss, next time you open Sublime Text you’ll be back where you were, with unsaved changes and files still intact. This is something that always happened, including in 1.x.
I’m planning on adding some API support for notifying plugins when focus is lost, and I’ll add a save_on_focus_lost plugin at the same time. No ETA on this though.