Do I have to worry about phones becoming obsolete because of a potential lack of OS updates?

[AC Question]

So I'm used to the iPhone method of OS updates, any phone from the last 5 years can update to the latest version of iOS, older phones are out of luck. One phone still in use in my family is an iPhone 4, which is out of luck... and so I run into apps that won't update or install on the phone any more. And so I'm thinking of replacing it with a Moto G4.

But I'm not real clear on OS update availability on Android phones, it seems like I've always heard it's a YMMV situation. If I buy any Android phone that comes with Marshmellow installed, am I pretty certain it'll get updated to Nougat or is it up to the whims of the gods? How far back are most apps supporting?

 

[belodion]

System upgrading varies with manufacturer. The best devices for up-to- date versions of the OS are the Nexuses. At present, the Nexus 4 has been supported up to Lollipop, the later devices are on Marshmallow.