Beta testers who are members of Apple's beta testing program receive the iOS 11.4 beta update wirelessly after installing the appropriate certificate on an iOS device.
Those wishing to participate in the beta testing program can sign up for Apple's beta testing site, which gives users access to iOS, macOS, and tvOS betas. iOS betas are not always stable and should not be installed on a primary device.
The beta version of iOS 1
The update includes support for AirPlay 2 features that allow you to play the same song on multiple devices and add Apple TV and AirPort Express-connected speakers to the Home app.
iOS 11.4 reinstates messages on iCloud. News on the iCloud was available during the beta testing period of iOS 11.3 but has not been released. Messaging on iCloud saves your iMessages to iCloud rather than to every device, improving synchronization features. Inbound incoming iMessages are currently being sent to all devices that you have signed in to with your Apple ID, but there is no true cross-device synchronization.
iCloud News allows you to download all your iMessages on new devices. When a message is deleted on a device, it is removed on all devices. Older messages and attachments are also stored in iCloud, not on the device, saving valuable storage space.
The latest beta release introduces a new (PRODUCT) RED background image on the iPhone 8 and 8 Plus and removes stereo sound on the HomePod that was in the first beta.