For the first time, Intel publicly confirms not only the existence of the X399 but also the Z390. The former is a next-generation high-end desktop platform (HEDT) chipset. The slide seems to suggest the X399 is for Coffee Lake-X and Cannon Lake-X, whereas previous rumors talked about Cascade Lake-X. The naming is confusing as AMD already has a chipset called X399. Perhaps Intel will pick a different name for the final production part.
Next we have the Z390, we've already heard some rumors about this chipset and the Intel documentation confirms it will support Cannon Lake and Coffee Lake CPUs. According to the rumor mill, we may see the Z390 chipset launch in combination with the first eight-core Coffee Lake processors. Cannon Lake is the first 10nm generation from Intel.
The chip giant announced at CES 2018 that it started shipping Cannon Lake before year-end 2017, but so far these chips haven't been seen in the wild. Yet another indication that Intel's 10nm process is still broken.
We don't know a launch date for the Z390 and X399 but it's safe to assume we'll know more by Computex.