"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Seeds Fourth Beta of iOS 11.4 to Developers [Update: Public Beta Available]
Registered developers can download the new iOS 11.4 beta from Apple's Developer Center or over-the-air once the proper configuration profile has been installed from the Developer Center.
The iOS 11.4 update introduces a new ClassKit framework for educational institutions, which supports new features announced at Apple's March 27 education-focused event.
For regular users, the iOS 11.4 update adds features that were originally present in the iOS 11.3 beta but removed ahead of release.
It includes support for Messages on iCloud, designed to store your iMessages in iCloud rather than on each individual device, allowing for improved syncing capabilities. Currently, incoming iMessages are sent to all devices where you're signed in to your Apple ID, but there is no true cross-device syncing.
Messages on iCloud will allow you to download all of your iMessages on new devices, and a message deleted on one device will remove it on all devices. Older messages and attachments are also stored in iCloud rather than on-device, saving valuable storage space.
The iOS 11.4 update also includes AirPlay 2 features, with the Apple TV once again available in the Home app. With AirPlay 2, the same audio content can be played in multiple rooms on devices that support AirPlay 2. AirPlay 2 includes a feature that lets you ask Siri on one device to play content on another AirPlay 2-enabled device. So, for example, you can ask Siri on iPhone to play content on your Apple TV in another room if you're running the iOS 11.4 and tvOS 11.4 betas.
There were initially signs of support for HomePod stereo sound in the first iOS 11.4 beta, a long-promised feature, but stereo sound didn't work properly and the mention was removed in the second beta. It's not clear if it will return for the update's release.
For the iPhone 8 and iPhone 8 Plus, there is a new (PRODUCT)RED wallpaper available, which is not available on iPhone X.
iOS 11.3, the previous update to iOS 11, introduced a new Battery Health feature for monitoring the status of your iPhone's battery, Business Chat for iMessage, which lets you communicate with companies directly in the Messages app, ARKit 1.5 with augmented reality improvements, new Animoji on iPhone X, Health Records from participating medical providers, and more.
Update: Apple has made a new version of iOS 11.4 available to public beta testers.