IS-2 model 1943 (IS-122) - 1943 model, armed with A-19 122mm gun.
IS-2 model 1944 - 1944 model with D25-T 122mm gun, improved frontal hull armour using thinner armour with a more efficient shape.
IS-2M - 1950s modernization of IS-2 tanks.
IS-3 - 1944 model redesign with new rounded turret, angular front hull casting, integrated stowage bins over the tracks. Internally similar to IS-2 model 1944, and produced concurrently. ~350 were built during WWII.
IS-3M - 1952 modernized version of IS-3. Fitted with additional jettisonable external fuel tanks and improved hull welding.