1 October 2021
Joomla version 4.0.3 is now available (major release).What's New in Joomla 4.0.3
Joomla 4.x is a major version. Everything has been redesigned, rethought, and has new features.
Joomla 4.x requires manual migration from Joomla 3.10 and earlier. For migration information please reference https://docs.joomla.org/Planning_for_Mini-Migration_-_Joomla_3.10.x_to_4.x. At the bottom of that page, you can then proceed to the step by step instructions for migration from 3.10 to 4.x.
Joomla 3.10 will continue to be supported for 2 more years.