Actually, almost 100% if it has not shipped. I've never heard of a case where Apple ships a discontinued model after the replacement has been announced. The only exception would be if the buyer ordered the old model after the new one was announced.
If they do ship you an old model you can take it to an Apple retail store and see if they will exchange it for the model. My guess is though that you'll see your order changed automatically by sometime tomorrow to reflect the new model.