In 1943, the Soviet Union began work on several new heavy tanks of theoretically superior design to the IS-2, which had just entered production. Object 701 was basically the same thing as the IS-2, only larger. Object 703, however, changed the design radically, and entered production in 1945 as the IS-3, while Object 701 entered production in 1946 as the IS-4. However, there were many more designs proposed than had ever been built, such as Object 701-1, which used the same hull as the IS-4, but with different running gear, engine, and transmission, all for the purpose of driving a heavier vehicle with an enormous turret that could carry a lot more ammunition and had much greater elevation and depression of its main gun.
Ordering the small variant will give you a single tank.
Ordering the medium variant will give you two tanks.
Ordering the large variant will give you five tanks.