Previewed at WWDC, launching in the fall.
iCloud Messages Returns to iOS in First Beta of iOS 11.3
It was not clear if and when the feature was actually going to be implemented, though, as Apple stripped all mentions of it from the iOS 11 website.
As of iOS 11.3, Messages in iCloud is back and is available for "testing and evaluation purposes," marking the official return of the feature. According to Apple's release notes, once iOS 11.3 beta 1 is installed, Messages will prompt users to turn on Messages in the Cloud when it is first launched.
Messages in the Cloud is automatically enabled for users who have two-factor authentication and iCloud Backup enabled, says Apple.
The new Messages in iCloud feature will be a welcome change for iPhone, iPad, and Mac users who prefer not to delete their messages. Over the course of several years, Messages can take up a lot of space. That space can now be freed up with the bulk of older messages stored directly in iCloud rather than on-device.