And Macbook Air isn't 12 hours all the time
http://www.macworld.com/article/204...rs-best-battery-life-of-any-apple-laptop.html
So expect actual battery life to be... pretty darn close to the older model.
I have a 13" 2013 MBA that I am about to return to wait for the 13" rMBP. I was getting over 17 hours per charge with web browsing and iTunes.