It only comes with one. If you disconnect both sides the I'd imagine the sway bar would hang down and shift side to side which isn't good or needed. Disconnecting the one side is all that's needed since they will be independent.
If you are exchanging for the stock one, all you need is one.
If you are disconnecting the stock set-up, all you need to doo is disconnect one side. This way you can test it and see if you like it!
On the '13's and '14's, the bar doesn't slide back and forth when it is disconnected as there is still a fitting that remains on the bar. That fitting will flop around a bit but I don't think that is a problem.