Gigabyte X99-UD3 M.2 supports SATA and NVMe interfaces.
Gigabyte X99-UD3 M.2 supports SATA and NVMe interfaces.
Your PC has an M.2 slot with a PCIe NVMe SSD, and you're considering adding another M.2 NVMe drive like the Intel 660P. You can install both M.2 NVMe and SATA SSDs depending on your needs and space.
The manual and specifications for the device are your reliable resource.