I have just started a test game as the Soviets, so I can show you a few bits.
This is Turn 2, so 4 days in.
You can see the AI almost managed to complete the encirclement of my entire 3rd Army. In an act of considerable luck, though, 3rd Army was among the very few armies that managed to fully activate, so next turn I saved most of my units, the ones who stayed inactive were surrounded and eliminated in short order
(It is a factor of some variables, like front commanders and level of Red Army reform you have managed to enact that defines the chances of particular armies activating. Needless to say the command and control structure is not exactly up for the task when the whole thing starts, so being able to move fully with the 3rd Army was a much needed break)
On the second one I just wanted to show how the AI prefers to encircle cities before assaulting them - a key tactic as costly sieges are not really affordable!
The third one is from a couple of turns later, Lvov is already well behind the enemy lines (visible on top left).
Here you can see a much bigger envelopment attempted - the bulk of the Romanians are pushing north while the German armies north of my guys are looking for ways to envelope instead of just smashing into them headlong.
And here is that situation one turn later: you can see they couldn't go past Proskurow in force so ended up linking up and enveloping where they had the chance: