It's not likely to be a pure "performance" thing. The 6S, according to wikipedia [1], is the oldest phone containing an A9 chip, which has an image processing

It's not likely to be a pure "performance" thing. The 6S, according to wikipedia [1], is the oldest phone containing an A9 chip, which has an image processing unit, a coprocessor that can handle Siri voice commands, and an NVMe storage controller. It is also the minimum requirement for ARKit. I doubt very much that Apple is being arbitrary in their support cutoff for phones. If it's capable of the features they build into the OS, it gets support. If I had to make a guess, the next cutoff point (iOS 15?) is going to be a chip having the Bionic Neural Engine, which would make the iPhone 8 the oldest supported phone. [1] https://en.wikipedia.org/wiki/Apple_A9 https://en.wikipedia.org/wiki/Apple_A9