Xcode 9.4 adds support for developing apps with ClassKit
About Xcode 9.4 beta
Xcode 9.4 beta requires a Mac running macOS 10.13.2 or later.
Xcode 9.4 beta includes SDKs for iOS 11.4, watchOS 4.3, macOS 10.13.4, and tvOS 11.4.
9.4 版本已知的问题，不支持构建运行 tvOS 11.3
Xcode 9.4 beta does not support building and running on devices running tvOS 11.3. (39042488)
Asset Catalog Resolved an issue that could cause progress to get stuck while editing AR assets in an Asset Catalog. (38393995) Resolved an issue that could cause a crash when dragging a .gif image into a Sticker Pack in an Asset Catalog. (38820366) Instruments Resolved an issue where loading a saved trace could result in an empty Symbols… panel. (38813311)
Resolved in Xcode 9.4 beta – Swift Compiler Swift Compiler Swift now correctly handles the case where protocol methods or base class methods defined in Objective-C claim to take non-null arguments of type id in their headers, but get invoked with nil values at runtime