Xcode 9 - Simulator: Screenshots taken are not of correct resolution for ItunesConnect / AppStore Connect

In Xcode 9.1, go to Simulator Menu > Debug > Optimize Rendering for Window Scale. disable this option, now the screenshots will be in the right size (resolution).

That's a bug in Xcode 9 (and, I would say, in Xcode 8 as well; the idea that the resolution and size of a screen shot would depend on how you displayed the simulator window was always just plain wrong).

Update to Xcode 9.1. In Xcode 9.1, Command-S always gets the resolution (and size) right for the device represented by the simulator window.

For example, if I say Command-S on the iPad Pro 9.7-inch simulator window in Xcode 9.1, no matter how big the window is, I get a screen shot that is 1536×2048. Well, that's the correct size for a screen shot to be submitted to the App Store. Nothing else needs to be done.