Pi is known for it's deep dish, they have two ovens--one for deep dish and one for thin crust. There are six deep dish pizzas on the menu and five thin crust pizzas, but any of them can be ordered either way. You can also create your own pizza, choosing from a variety of toppings.
The "Pi Snacks" you may have seen on the menu are a D.C. exclusive, they are not available in the four St. Louis locations.
Their happy hour runs from 4:00 p.m. until 6:30 p.m. every day except Saturday. You can get Pi Snacks as well as $5 wines and $4 draft beers. Sure there are better deals out there, but there are 24 beers on draft at Pi.
The restaurant will also be open for brunch, serving pizzas with eggs instead of tomato sauce.
The menus are available here.