According to Lockheed Martin, the latest release is the most optimised and stable version yet.
New features include support the consumer versions of the Oculus Rift and HTC Vive. Both Virtual Reality (VR) headsets seamlessly integrate into the application. New VR enabled views automatically become available when a headset is connected to your PC and fully support head tracking, positioning and stereoscopic rendering. New VR views can also be easily added and configured through the Camera SDK.
A new Cinematographer control mode is now available giving unrestricted and precise camera control to capture any angle at any time. Direct Input support is back alongside Raw Input giving users more options on how to configure their input devices. Additionally, a new Navigation Visuals screen can be used to toggle facility and airspace overlays directly on the 3D world.
The Professional Plus version has been updated with features including weapons support for avatars, multiple enhancements to DIS including multiplayer support, voice communication, and easier configuration, as well as improved multi-channel stability.
Developers have even more tools available at their disposal including easier Scaleform integration into views, Lua support in ModelDef.xml files, custom light rendering via the PDK, the ability for plugins to register with internal events in the application, as well as numerous other advanced features.
The Prepar3D v3.4 is available for free if you have a valid Prepar3D v3 license.