We don’t recommend it. While the Lightning connector of the 12.9" iPad Pro is compatible, its overall size is a bit too big to be stable on the HiRise.
COVID-19 Virus Update: Twelve South remains open and appreciates your continued support and business immensely. However, due to our team working remotely, the only way to reach us is via email. We monitor email closely and will typically reply the same day during normal business hours (see below). Please reach out with your order number, concern or question at firstname.lastname@example.org.