Apple has released the first beta versions of iOS 11.1, macOS 10.13.1 High Sierra, tvOS 11.1, and watchOS 4.1. Each update is available now for users participating in the developer beta testing programs.
The easiest way to get the beta updates of iOS 11.1, macOS High Sierra, tvOS 11.1, and watchOS 4.1 are through the over-the-air software update mechanisms. If you’re a developer and have not yet enrolled an eligible device with a beta profile, you can do so at the Apple Developer Center website.
iOS 11.1 developer beta 1 is available now through the software update mechanism within the Settings app of iOS.
macOS High Sierra 10.13.1 developer beta 1 is available as an update through the Mac App Store Updates tab.
watchOS 4.1 beta 1 and tvOS 11.1 beta 1 are also available now from their respective software update mechanisms.
Beta operating systems are notoriously unreliable and unstable, and thus not fit for regular users. Always back up a device before installing beta system software.