Apple is currently testing many beta versions of its platforms, including updates iOS 11.4 and iOS 12.
The company officially released the second beta version iOS 11.4.1 to developers today. It can be downloaded and installed over the air using the Software Update mechanism if you have a developer account. Also, the update can be downloaded directly from the website Apple for developers.
If you have a suitable profile installed, you can download the update in Settings -> General -> Software update. Click Install and follow the instructions on the screen.
Apple has also released the second beta of macOS High Sierra 10.13.6, which can be downloaded from the Updates tab on Mac App Store. Together with it, the second beta of tvOS 11.4.1 was released. You can install the update through Xcode. If you have Apple TV 4th or 5th generation, you can enable auto-update, which will also download the beta version if you have a developer profile.
In each case, the updates are minor and do not contain any new features or changes. They are aimed at fixing bugs and improving performance.