The Dev Server is not open yet, but you can download most of it now to version 1.53.6.9
http://launcher.warthunder.com/wt_dev_launcher.exe

It is best to do it now rather than wait for it to open. It took me one hour on a 20mbps modem.
If you wait until it opens you will miss a lot of playing time.
If you update now, all you will need is a small patch when it opens and you are ready to rock n' roll.