Earlier this week, Apple has released the third beta for iOS 11.3 to registered developers, the main release for public is expected to launch this spring, presumably in March. The new update is mainly focusing on ARKit improvements, adding AirPlay 2 as well as the new battery reporting features.
So far, the only thing that is different with this release, is support for the iPod touch and the weird omission of all the AirPlay 2 features, hopefully meaning they will return in a later beta release. Also, in the settings app, you can now edit the the privacy settings of the Health Record feature, which is also new in iOS 11.3
The new update finally brings Messages on iCloud, a feature which was promised to arrive with the initial launch of iOS 11 back in June 2017. Messages on iCloud allows all of your devices to keep iMessages in sync, when a message is read or deleted your Mac, iPhone and iPad will reflect those changes.
iOS 11.3 also brings a new revised version of ARKit, which is now intelligent enough to recognise weird shaped surfaces as well as walls.
For iPhone X only, Apple has added four new Animoji characters, Lion, Brown Bear, Dragon and a Skull.
Source: Apple Newsroom