I am pleased to announce that Qt 5.12 Alpha is released today. There are prebuild binaries as well in addition to source code packages with Alpha release.
Please check Qt 5.12 New Features wiki to see what new is coming with Qt 5.12 release. Please note that the feature list is still in progress and not to be considered final before the first Beta release.
Our target is to start releasing regular beta releases quite soon after this Alpha release. First beta release should be out within few weeks, see details from 5.12 wiki.
Most importantly, remember to give us feedback by writing to the mailing lists and reporting bugs to Jira.