Uh, the war on the ground in Donbas? Or was that a trick question.

On a long enough time scale, every gain is "ephemeral." That being said, Russia is using very different tactics for what appears (I don't have secret knowledge of Russia's actuals plans) to be a very different strategy than the one(s) they followed the first two months of the war.

Russia appears to be going to their proven strategy of long war and attrition. They are taking the time and resources to create layered defenses behind their front lines (unlike what they did around Kharkiv) to provide close fall-back positions.

Of course Russians are dying. Right now a lot more Ukrainians appear to be dying than Russians. That is a strategy that ends in Ukrainian defeat.