Apple announced in a press release earlier today several new features to come with iOS 11.3, including new Animoji and health records in the Health app.
One feature that was not announced in the press release but is available in this beta is the much-anticipated Messages in iCloud, which first appeared in the first developer betas of iOS 11 and macOS High Sierra, but was removed later because it was not ready for production.
With Messages in iCloud, users can see their full Messages history on all devices, even after being disconnected for a long period of time.
With the release of iOS 11.3 beta 1 and corresponding developer release notes, Apple announced that iOS 11.3 includes the Messages in iCloud feature. Messages will prompt users to turn on Messages in iCloud on first launch after upgrading to beta 1. Users with two-factor authentication and iCloud Backups enabled will get Messages in iCloud enabled automatically.
iOS 11.3 beta 1 is available as a developer beta today and should become available as a public beta soon.