SummaryPrevious studies suggest that postautologous stem cell transplant (ASCT) recovery of polyclonal immunoglobulin from immunoparesis in patients with multiple myeloma is a positive prognostic marker. We performed a longitudinal analysis of polyclonal immunoglobulin concentrations and unique B‐cell sequences in patients enrolled in the phase 3 ATLAS trial that randomized 180 subjects to either carfilzomib, lenalidomide, dexamethasone (KRd) or lenalidomide (R) maintenance. In the KRd arm, standard‐risk patients with minimal residual disease negativity after six cycles de‐escalated to R alone after cycle 8. One year from the initiation of maintenance at least partial recovery of polyclonal immunoglobulin was observed in more patients on the R arm (58/66, p < 0.001) and in those who de‐escalated from KRd to R (27/38, p < 0.001) compared to the KRd arm (9/36). In patients who switched from KRd to R, the concentrations of uninvolved immunoglobulin and the number of B‐cell unique sequences increased over time, approaching values observed in the R arm. There were no differences in progression‐free survival between the patients with at least partial immunoglobulin recovery and the remaining population. Our analysis indicates that patients receiving continuous therapy after ASCT experience prolonged immunoparesis, limiting prognostic significance of polyclonal immunoglobulin recovery in this setting.