From July 2018 all apps submitted to App Store will need to support iPhone X and be built with iOS 11 SDK


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Apple have announced that all applications submitted to the store from July 2018 will need to support the Super Retina display of iPhone X and be built with iOS 11 SDK

Upcoming iOS 11 App Update Requirements
May 7, 2018
iOS 11 delivers innovative features and the redesigned App Store to hundreds of millions of customers around the world. Your apps can deliver more intelligent, unified, and immersive experiences with Core ML, ARKit, new camera APIs, new SiriKit domains, Apple Music integration, drag and drop for iPad, and more. Starting July 2018, all iOS app updates submitted to the App Store must be built with the iOS 11 SDK and must support the Super Retina display of iPhone X.

Official Apple announcement here:
https://developer.apple.com/news/?id=05072018a