According to this website the Ryzen 19xx CPU has 64 PCIe lanes but 4 PCIe lanes are used for the X399 chipset.
That leaves 60 PCIe lanes for Motherboard manufacturers to play with when designing their motherboards for the Ryzen CPU. AMD's Ryzen Threadripper 1950X, Threadripper 1920X, and Threadripper 1900X CPUs revealed - The Tech Report - Page 1
This website shows the same thing for the Rzyen 2xxx CPUs : The AMD Threadripper 2990WX 32-Core and 2950X 16-Core Review
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