A major result of Blumberg-Gepner-Tabuada from 2013, based on work of Cisinski-Tabuada of a few years prior, provides a way to think about algebraic K-theory as the universal additive invariant of stable infinity categories. This talk will explain in plainer terms what that means and how it connects to classical results of Quillen and Waldhausen. Time permitting, I will also discuss results proven using this new language that (thus far) have no `non-infinity' proof.