Currently Apple is testing many beta versions of system updates, including iOS 11.4 and iOS 12.
Today Apple officially released the third public and beta versions for developers of version iOS 11.4.1. The update can be downloaded 'over the air' using the Software Update mechanism or from the website Apple for developers.
You can download the developer version if you have a suitable profile installed on your device, and the public version if you are registered in the beta testing program. To do this, go to Settings -> General -> Software Update and follow the instructions on the screen.
The company also released the second beta versions of tvOS 11.4.1. To install the update, you need to connect Apple TV to your computer and use Xcode, or enable auto-update on 4th and 5th generation devices.
In addition, Apple has released the third beta of macOS High Sierra 10.13.6 to developers. The update can be downloaded from Mac App Store or from the developer site.
In all cases, the updates are minor and do not contain any new features. They are aimed at fixing problems and fixing bugs, as well as improving performance.