Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 10-inch Bundt® pan.
Mix cake mix, pudding mix, vegetable oil, sugar, water, and eggs together in a large mixing bowl until smooth. Fold in sour cream; batter will be very thick.
Pour 1/2 of the batter into the prepared pan. Sprinkle 1/2 of the toffee bits over the top, being careful to keep them away from the sides of the pan. Pour remaining batter over top, then sprinkle with remaining toffee bits.
Bake in the preheated oven until a skewer inserted in the center comes out clean, about 55 minutes.
Cool on the pan for 5 minutes, then invert onto a serving plate and let cool for about 25 more minutes.