Download the SDK

How do I download the SDK?

Tell me how

The SDK for what? If you’re referring to the Apple-provide language compilers and linker, then get that from from App Store Xcode download as mentioned above, or enroll in the developer program and download Xcode or the command line tools from the Apple Developer program download website.

If you’re looking for, for instance, the visionOS tooling or the game porting tooling, that’s available via the developer program website.

Or for learning and using Swift, Playgrounds app for macOS or iPadOS.

There’s not much for development directly on and locally to iPhone, though.

Go the app store and get XCode.