Qt version history

The latest version of Qt is 6.0 from December 8, 2020.
5.12 LTS, which was released on 6 December 2018, is supported for three years.
5.9 LTS, which was released on 31 May 2017, is no longer supported – support ended 31 May 2020.
Qt 4.
Qt 4 was first released in 2005 and has been unsupported since 2015.
Qt 5.
Qt 5 was officially released on 19 December 2012. This new version marked a major change in the platform, with hardware-accelerated graphics, QML and JavaScript playing a major role. The traditional C++-only QWidgets continued to be supported, but did not benefit from the performance improvements available through the new architecture. Qt 5 brings significant improvements to the speed and ease of developing user interfaces.
Framework development of Qt 5 moved to open governance, taking place at qt-project.org. It is now possible for developers outside Digia to submit patches and have them reviewed.
Qt 6.
Qt 6 was officially released on December 8, 2020.