To be honest, everything you need to know about the new World of Tanks update is contained in the video above. It explains how Domination mode is expanding with new events: Steel Hunt and Supply Swarm. It sets out the rules of each, like how, in Steel Hunt, four platoons of three players will attempt to deliver flags to their bases.
The video also details the changes to the Swamp map, and the graphical improvements to shadows and water being implemented for both Standard and High Quality clients. It even details the two new tanks—the Spähpanzer 1.C and the Heavy Tank No. VI.
All of which means there's really not much left for me to do except link the full patch notes (opens in new tab) and say that Update 9.9 is out now.