I can't tell. D's idea that we'd get both is fairly compelling, though.
All the class updates to date have been of a style that could realistically get in and bundle at close range. The sniper just can't. They also know by now that people will play the updated class like maniacs for the first couple of weeks. Imagine matches filled with mostly snipers...? They'd be SOOOO tedious.
So, why not add the sniper's worst enemy, the spy to keep things mixed up?
I'd like this to be a two class update and I think that's what we're being shown.
But, on the main page of the team fortress site where it lists all the big updates, there is a listing for the Spy, but not the Sniper. I'm sure we'll find out soon enough, but I'm betting the "Spy Update" contains Sniper upgrades as well.