That’s correct, SuperCruise is not related to V2V or V2X, which is only available on the CTS (starting with the 2017 model year).
At the end of the day, SuperCruise is a real-world technology that works while V2X and V2V is significantly more experimental and has very little practical real-world applications.
But yes, it is strange that the CT6 doesn’t include V2X/V2V, as the CT6 is Cadillac’s foremost model. We’ll see if the 2019 CT6 gets it. It’s currently unclear, and hasn’t been announced by Cadillac, but that doesn’t necessarily mean that it won’t be available.
