VEX announced the new V5 system at CES in Las Vegas in January 2018. The new V5 system is a complete replacement of the electronics and programming system upon which VEX competitions are based.
There have been issues with the V5 rollout, but there are many exciting things that VEX did well with the V5.
It has much stronger motors, a much better brain, and the addition of a couple features such as a Vision Sensor, better wiring, and other improvements.
To see all the current and planned features of the V5, see this page:
VEXos is the operating system the V5 Brain runs on. Completely designed by VEX, it is the foundation that all the V5 programming languages work with. It provides assess to the motors, sensors, and controller in an unified API.
This changes how we interact with the V5. With the Cortex, we just set power to the motors and read from sensors. However, with Smart Motors, we can just tell them what to do and they will control their own power. An example of this is PID: now VEXos just tells the motor to move 2 rotations and the motor will execute that movement itself.
All programming languages for V5 have common wrapper functions that tell VEXos what to do.
VEXos receives regular updates from VEX to fix various bugs or improve features. VEXos can be updated a few ways, described on the VEXos Updates page. It is important to always keep your V5 at the latest version, as some of the updates have been to fix some pretty serious battery issues.