2 expansion slots, 1 pci express x16 slot (x16 link), 2 pci express x8 slot (x8 link) – Asus TS300-E8-RS4-C User Manual

Page 62: 3 pci express x1 slot (x1 link), 5 pci slot, Expansion slots -6 4.2.1, Pci express x16 slot (x16 link) -6, Pci express x8 slot (x8 link) -6, Pci express x1 slot (x1 link) -6, Pci slot -6