Qt 5.11 Alpha is released today. As usual the official Alpha is a source code delivery only, but later we will offer development snapshots of Qt 5.11 regularly via the online installer.
Please check Qt 5.11 New Features wiki to see what new is coming with Qt 5.11 release. Please note that the feature list is still in progress and not to be considered final before the first Beta release.
Next milestone in our way to final Qt 5.11 release (which is planned to happen in May) will be first Beta release. We are targeting to get it out as soon as possible soon after the Alpha. We will release several Beta releases in similar manner as before, available via the online installer.