Some of the changes are fairly obvious:
There are nine Actions instead of twelve, which means the starting default is five dots instead of seven.
A lot changes from Deep Cuts have been incorporated, like how Action Rolls work is now Threat Rolls are in that, with possible multiple outcomes, although they are still called Action Rolls and it's expected you will sometimes have to roll to actually do the thing. Likewise, Push Yourself is from how it works in Deep Cuts.
There are no playbooks, mostly because the setting is so flexible. Players can start their characters however they want. The functionality of 'Fine' equipment from playbooks is instead incorporated into selectable Aptitudes and Knowledge, which give you increased Effect on rolls that do certain things or when you need to know certain things.
The biggest change: This game is not grim and gritty, which means that Stress is short term and Trauma is gone.
There's less Stress available, at least it looks like that, but once you realize how Distinctions work you realize you get to clear three extra Stress with trivial roleplay. So there's basically still nine Stress. And you get to clear even more Stress with Distinctions if you're willing to accept negative consequences for a roll.
A less obvious change is that there is no required Trauma for full Stress, and you do not have to work to clear Harm between sessions, it just clears. This will alter the cost of Harm in a fairly serious way, and is intended to make the game much less serious. You also generally don't have to reduce Stress in downtime, as you get a lot of that for free.
Additional, as Stress and Edge are basically 'How realistic but awesome is this character to the imaginary audience?', Edge does not have to follow narrative rules and you can use it to help other people in ways that do not have to make sense, because you're looking so cool you can get away with plotholes.