Two tapeouts, one for the IO die and one for the 8-core chiplet. For lower core count versions they can simply leave chiplet slots blank: https://img.purch.com/o/aHR0cDovL21lZGlhLmJlc3RvZm1pY3JvLmNv...
Epyc IO die will probably be re-used on Threadripper with chiplet slots blank though.