ESPN.com has the story. Chris Sheridan also speculates on who the frontrunner to be Stern's replacement is:

Silver would be better than Granik in the top spot, in my opinion. Russ, despite being absolutely hilarious during every season's draft lottery, is too old-school to push the league forward.I'm not ready for the Stern reign to end, though. I'm actually nervous about what'll happen when it does. I'm not anti-union or anything, but with Stern and Granik gone, there's no question Billy Hunter and his guys will make a massive power play. I hope they fail, for the good of the sport.