This Soviet mechanized artillery is somewhat like the German Stug III because it was directly inspired by it.
Let’s take a quick look at an idea that worked well for both combatants.
The basic idea here is simple enough. This is self propelled artillery that can accompany infantry or other mobile formations. Its mobile so no lengthy set-up period is involved, and its armored in the expectation it will be far closer to the front lines than normal artillery is. Note this is different from a tank in several regards, the most noticeable difference being no turret. The gun is fixed to the hull of the vehicle, that is simpler, cheaper, and allows for a bigger gun on any particular vehicle. And the main weapon is a field gun or howitzer, not specifically an anti-tank gun.
In April 1942 the Red Army requested an armored, mechanized gun after seeing how effective the German Stug III could be. They wanted a common 76 mm field gun and a 122 mm howitzer (a howitzer uses a shorter barrel for high angle fire that can shot behind a wall, into a foxhole, or on the reverse slope of a hill). The 76 mm gun led to the Su-76 on a T-70 tank chassis; while the 122 model was built on a T-34.
Through 1943 638 of them, tagged “Su-122” were built. This was considered adequate for the need, attrition was expected to be fairly slow because of how they were used. The vehicle was built on a T-34 hull, which of course was considered an excellent starting point. This ensured it was reliable and fast enough. The Soviet 122 mm howitzer actually allowed for direct sighting (in addition to its normal indirect fire mode) for an anti-tank function. A HEAT (High Explosive, Anti-Tank) round was developed for the anti-tank role, but it was found the standard High Explosive round had enough mass and concussive explosive force that the special round was not needed.
Keep in mind that a howitzer in direct fire role would not be accurate at a very long range, so this was more of an emergency back stop for when opposing tanks had achieved a break through. The Soviets later built an Su-85 that was a pure tank destroyer on the same chassis. In fact, just like the anti-tank versions of the Stug III, the Su-85 was ultimately built in far greater numbers than the Su-122.
Which leads to saying the Su-122 was only a limited success. It did put a big gun, in an armored shell right with the Infantry. But rate of fire was slow and crew function was clumsy (too many men needed for basic operation). Attempts were made to put a more efficient howitzer on the vehicle, but ultimately this was not ideal either. Post-War a small number of T-54 tanks were built as a Su-122/54, but that is a whole different vehicle.
Those Su-122 produced were expended or worn out during the War and today, only a single example at the Kubinka Tank Museum is known to exist.
This example served at Kursk, Summer of 1943. It is from the Tamiya kit and was a simple build.