The tank rental feature is currently being tested. After its rental, the premium tank can be bought with a discount. At the moment, 7 day and 30 day rentals are available. Each next rental is cheaper.
Screencaps (only in Russian at the moment, unfortunately):
https://pp.vk.me/c836722/v836722571/f567/dT_9AElzZGs.jpg
https://pp.vk.me/c836722/v836722571/f570/jbBJQ3_T1sk.jpg
https://pp.vk.me/c836722/v836722571/f579/ednd6CQDbuI.jpg
