If Medvedev said that Russia was starting WW3 tomorrow I could sleep soundly knowing full well that Russia wasn't gonna do jack shit.

Generally the Russo Ukrainian War has had long periods of attritional fighting followed by rapid changes in territory when one side loses too many people to hold the current frontlines. So although it's a stalemate for now, things could change rapidly. Kherson was a months long slog with little signs of progress till the Russians suddenly retreated.