For more details see the Canonical announcement
For more information on Ubuntu on IBM servers
Read the FAQ for more information on this offering. A big difference from SUSE and Red Hat for z Systems is the pricing. Ubuntu is priced at $19,500 USD per drawer per year. That means on a z13s or LinuxONE Rockhopper you get 1 to 20 IFLs and on the z13 or LinuxONE Emperor you get 1 to 30 IFLs for that one low price. This should be a huge game changer for Linux on the mainframe.