This only seems to be for a special version of the X1 Yoga, not for all models in the X1 line. The new X1 Carbon is the same thickness as the previous generation: 14.9mm[1], though it looks like they reduced the bezels and redesigned the hinge.

1. See tech specs on this page: https://www.lenovo.com/us/en/coming-soon/X1-Carbon-G9/p/22TP...