Apple has released the first beta versions of iOS 11.1, macOS High Sierra 10.13.1, tvOS 11.1, and watchOS 4.1. The initial beta releases of system software are for developers only, but public beta versions of eligible system software beta builds will likely become available later.
iOS 11.1 beta 1 is available to download now for users enrolled in the developer beta testing program. The beta release will be available via the Settings app > General > Software Update.
macOS High Sierra 10.13.1 is available to download via the Mac App Store for Mac users enrolled in the developer beta testing program.
iOS 11.1, macOS High Sierra 10.13.1, tvOS 11.1, and watchOS 4.1 will likely focus on bug fixes and refinements to the operating systems. Additionally, the first point release updates may offer the inclusion of various features like Apple Pay over iMessage and iMessages in iCloud which were not included in the initial releases of iOS 11 and macOS High Sierra.
Apple typically releases multiple beta versions of system software before a final version is made available, thus it may be reasonable to expect a final version of iOS 11.1 or macOS High Sierra to be out sometime in late October or early November, perhaps around the timeline when iPhone X ships to customers.
The most recent non-beta versions of system software are currently iOS 11.0.1 for iPhone and iPad, macOS High Sierra 10.13 for Mac, watchOS 4 for Apple Watch, and tvOS 11 for Apple TV.