How can I get this App Store purchase window in my app?

I have implemented subscription IAP in my iOS app, but now my boss showed me several apps that provide a very nice purchase ActionSheet like window, when purchasing:

I only get simple Alerts that confirm purchase.

Is this a custom library? I see it in several apps, so it doesn't seem to be a pure custom design. Would love to use it as well.

Solution

The first image (The nice User Interface) of yours is from the latest iOS version (iOS 11). That screen gets displayed when you make a purchase in iOS 11. Previous versions will show you the second image for purchases. Get an iOS 11 device and go to App Store to download an app, and you'll get that new fancy UI.

To get that new UI, the app must be compiled with iOS 11 SDK.