Pro Display XDR works on iMac Pro at 5K, not 6K - Current Mac Hardware Discussions on AppleInsider Forums
Here's what we know so far about Apple's first 6K display coming this year
iMac Pro (2017) - Technical Specifications - Apple Support
Futureworld India - iMac Pro. Power to the pro. • 27-inch (diagonal) Retina 5K display • 5120‑by‑2880 resolution with support for one billion colors • Stunning 5-mm-thin design • 8-core Xeon W
Apple iMac Pro 5k (27") 3,2GHz 8Core Standard iMac Pro | MUSIC STORE professional
Apple 27" iMac Pro with Retina 5K Display Z14B-10C-32-4TB-56 B&H
Set my iMac Pro to 3840 x 2160 - Apple Community
Apple Starts iMac Pro Sales on Dec. 14: 8/10-Core Models At Launch, 14/18-Core Models Due in 2018