Only between 2 sources. Airpods can switch seamlessly between all my Apple devices without me needing to do anything. The only exception is my PC since I have to connect via Bluetooth.
As many as are synced via iCloud. I currently can switch between iPhone, iPad, Mac (multiples), Macbooks (multiples), and Apple TV and also Apple Watch. I also have them paired with my gaming PC and some gaming consoles but those don't automatically switch. I have to go into a Bluetooth menu and connect them but that's quick and no different from most Bluetooth headsets. The in-ecosystem stuff is the killer piece for me.
That's not the same thing. With Airpods, I can start a video on my iPhone, switch to my iPad for a bit, walk over to my Mac and listen for a bit, and then turn on the Apple TV and watch a show and they switch to every device seamlessly. If I use handoff from one device to the other, I can even do that same process with the same video and switch from device to device without doing anything with the Airpods.