https://www.polygon.com/2018/1/10/16874678/pokemon-go-ios-11-pokemon-go-plus-issues

Niantic will soon discontinue Pokémon Go support for iPhones that aren’t compatible with iOS 11, the latest version of the smartphone’s operating system. When that update launches in late February, players with older phones will either have to upgrade or give up on the game — even as current iOS 11-users continue to complain about Pokémon Go’s issues with the firmware.

The developer published a note to its Pokémon Go blog on Jan. 9 to give iPhone users a heads up. The text follows below.