My Cloud OS 5

I’m confused about the upgrade to OS 5. Is it an app software upgrade for my phone or is it a firmware upgrade? My Cloud firmware is 2.21.111 and it works flawlessly. My Android app is ver 4.4.28 and it works flawlessly. MUST I upgrade?
I appreciate everyone’s opinion. I ain’t yelling at anyone.
Thanks for the help and support.

Thanks for the reply. I would guess that the latest firmware takes care of the older stuff and the OS 5 makes it compatible.