All of the GFS is now running an FV3 model core (which is why people refer to it as the FV3). V16 is the coming upgrade to the GFS, this upgrade will actually change model physics vs the FV3 which just changed model capability and scalability. Because they need to test the V16 to ensure no bugs, it is run in parallel to the operational GFS to test performance. So the V16 and parallel are the same.