Apple seeded iOS 11.4 developer beta 4 for the iPhone, iPad, and iPod touch on Monday. So far, this release cycle for iOS 11.4 includes AirPlay 2, along with Messages in iCloud. HomePod stereo pairing was removed in developer beta 2. A new public beta release is available, too.
Apple has been pulling and putting features back in for the last few developer beta releases, and the presence of these features doesn’t necessarily mean they will be in the official release of iOS 11.4
Apple often adds and removes features in beta releases to test performance and look for bugs. We saw that with AirPlay 2 and Messages on iCloud in iOS 11.3. Both features were in betas, but were pulled before the official public launch last week.
You’ll need an Apple Developer Connection account to get the beta, or you can wait for the first public beta. That’ll likely come in the next few days.