What is app thinning? (iOS, tvOS, watchOS)
The App Store and operating system optimize the installation of iOS, tvOS, and watchOS apps by tailoring app delivery to the capabilities of the user’s particular device and operating system versions, with minimal footprint. This optimization, called app thinning, lets you create apps that use the most device features, occupy minimum disk space, and accommodate future updates that can be applied by Apple. Faster downloads and more space for other apps and content provides a better user experience.
Slicing (iOS, tvOS)
Slicing is the process of creating and delivering variants of the app bundle for different target devices and operating system versions. A variant contains only the executable architecture and resources that are needed for the target device and operating system version. You continue to develop and upload full versions of your app to App Store Connect. The App Store will create and deliver different variants based on the devices and operating system versions your app supports. Use asset catalogs so that the App Store can select images, GPU resources, and other data appropriate for each variant. When the user installs an app, a variant for the user’s device and operating system version is downloaded and installed.
Xcode simulates slicing during development so you can create and test variants locally. Xcode slices your app when you build and run your app on a device or in Simulator. When you create an archive, Xcode includes the full version of your app but allows you to export variants from the archive.
Note: Sliced apps are supported on devices running iOS and tvOS 9.0 and later. Otherwise, the App Store delivers universal variants to customers. Universal variants are also delivered through Mobile Device Management (MDM), apps purchased in volume through Apple School Manager or Apple Business Manager, or apps downloaded using iTunes 12.6 or earlier.
Bitcode
Bitcode is an intermediate representation of a compiled program. Apps you upload to App Store Connect that contain bitcode will be compiled and linked on the App Store. Including bitcode will allow Apple to re-optimize your app binaryin the future without the need to submit a new version of your app to the App Store.
For iOS apps, bitcode is the default, but optional. For watchOS and tvOS apps, bitcode is required. If you provide bitcode, all apps and frameworks in the app bundle (all targets in the project) need to include bitcode.
Xcode hides your app’s symbols by default, so they are not readable by Apple. When you upload your app to App Store Connect, you have the option of including symbols. Including symbols allows Apple to provide crash reports for your app when you distribute your app using TestFlight or distribute your app through the App Store. If you’d like to collect and symbolication crash reports yourself, you don’t have to upload symbols. Instead, you can download the bitcode compilation dSYM files after you distribute your app.
On-Demand Resources (iOS, tvOS)
On-demand resources are resources—such as images and sounds—that you can tag with keywords and request in groups, by tag. The App Store hosts the resources on Apple servers and manages the downloads for you. The App Store also slices on-demand resources, further optimizing variants of the app.
On-demand resources provide a better user experience:
App sizes are smaller so apps download faster, improving the first-time launch experience.
On-demand resources download in the background, as needed, while the user explores your app.
The operating system purges on-demand resources when they are no longer needed and disk space is low.
For example, an app may divide resources into levels and request the next level of resources only when the app anticipates that the user will move to that level. Similarly, the app can request In-App Purchase resources only when the user makes the corresponding in-app purchase.
Note: If you distribute your app to registered devices (outside of the App Store), you must host the on-demand resources yourself.
To set up on-demand resources in your app, read On-Demand Resources Guide and NSBundleResourceRequest.
