You can use Split View and Slide Over with Horizon Client on any iPad model that supports Split View and Slide Over and is running iOS 9.x.
With Split View and Slide Over, you can open Horizon Client and another app at the same time. You can run Horizon Client as either the primary app or the secondary app.
If you rotate your device or slide the vertical divider that separates the primary and secondary apps, Horizon Client automatically adjusts to fit the size of the window. If you are connected to a remote desktop, the remote desktop automatically adjusts to fit the size of the window if the Resolution setting is set to Auto - Fit. For information about setting the resolution for a remote desktop, see Changing the Display Resolution Setting.