According to Techpowerup the range features more core-counts and is to answer the rise of the second generation AMD Ryzen "Pinnacle Ridge".
"Whiskey Lake" was planned for Q1-2019 alongside the 14 nm original Z390 chipset however it is pretty clear that Intel wasn't expecting AMD to rebound with Ryzen 2000 series and thought it was a good idea to rush through with a new product generation yet again.
The Z370 is being re-branded to Z390 (with an improved CPU VRM reference design), and what was meant to come out in Q1-2019, could come out by Q4-2018. It has been suggested that Intel would have come out sooner had not its distributors been saddled with large amounts of unsold 8th generation Cores. Besides motherboard vendors aren't fully ready for the chip and getting a 9th gen Core chip doesn't warrant a new motherboard, customers would be inclined to pick up 9th generation chip with their existing boards, or any new 300-series board.
No one in their right mind would buy an 8th generation Core CPUs at this rate. In fact, some laptop makers are still flogging 7th generation cores.
Intel's answer to this issue is to have a paper launch of 9th generation Core on 14 August. The launch will be limited to three SKUs: Core i9-9900K, Core i7-9700K, and Core i5-9600K. Of these, the i9-9900K and the i7-9700K are the first 8-core processors by Intel on the mainstream-desktop platform; while the i5-9600K is a 6-core chip that's largely unchanged from the current-generation Core i5 chips.