Apple announced 12.9 inch iPad pro on September 9th 2015 at a special event in Gold Solver and Space gray color selections. iPad pro priced from $799 to $1299 for 32, 128 and 256 GB internal storage. iPad pro has basically two models as WiFi only and Cellular + WiFi whic is both models are featuring with A9X chip and Apple M9 motion co-processor.
iPad pro initially shipped with iOS 9.1 and the latest compatible iOS version for iPad pro is iOS 9.3.1. Importantly You can’t downgrade or upgrade any iOS version between iOS 9.1 and 9.3.1 at the moment because Apple is only signs iOS 9.3.1 for compatible devices right now. Within the above iOS range there may be iPad pro devices which is eligible for Cydia download and some of are not compatible for jailbreak. See the following chart for more details.
For further clarification, you can only Download Cydia only on iOS 9.1 running iPad pro. There is no jailbreak tool for Cydia download iOS 9.3.1, 9.3 or 9.2. If you are interested in iOS beta testing, you can install iOS 9.3.2 public beta on any iPad pro, but still you can’t have Cydia.