On November 2nd QGIS 3.4 ‘Madeira’ was released. It is the first long-term release in the new 3.x platform. To install it you can visit the QGIS Download page. Installers are ready for Windows, Max OSX and Linux.
Remember QGIS always has two main versions available. There is the long-term release, which is the most stable because it is supported for one calendar year. In addition there is always a latest release. QGIS 3.4 falls into this former category.
This is a great time to update your version of QGIS. Especially if you are still using the 2.x line. QGIS 3.x is fast, stable and feature rich. If you are still a 2.x user there is a huge list of new features and useful changes. At this point most of the popular plugins have been migrated over from 2.x to 3.x. The chart below shows the steady migration and growth of 3.x plugins. You can review the visual changelog for this version here. You can also find the changelogs for versions 3.0 and 3.2.