Here, we present a resolution to the apparent dilemma when both comonomers undergo equilibrium polymerization by keeping track of comonomer sequence information implicitly at each position in the chain as a probability mass function describing the eight possible dyads. In this way, the identity of the antepenultimate chain unit revealed by a depolymerization reaction of the n th chain position is accounted for stochastically based on the population of dyads ending at the (n -1) th position. This treatment relies on the assumption that the rates of depropagation reactions from each possible terminal dyad do not depend on the identity of the antepenultimate monomer, which is true under the penultimate model of equilibrium copolymerization (Scheme 1). Compared to explicitly tracking all monomer sequences, this approach requires significantly fewer equations (approximately 8𝑛 versus 2 @ ), does not require any assumptions regarding previous sequence information, yet maintains accurate predictions of comonomer consumption rates (see the Population Balance Kinetic Modeling Section of the Supporting Information for details).