The large Classic Pepperoni and large Classic Cheese Pizzas are the chain's original $5 Hot-N-Ready Pizzas (and are still normally $5 each). They switched to calling them "Classic" pizzas (rather than just the Pepperoni Pizza and Cheese Pizza) when they introduced their ExtraMostBestest Pizzas in 2017.
The $3.99 pricing is limited to three pizzas per person per day.
Photo via Little Caesars.