A Study to Evaluate Mezigdomide in Combination With Carfilzomib and Dexamethasone (MeziKD) Versus Carfilzomib and Dexamethasone (Kd) in Participants With Relapsed or Refractory Multiple Myeloma (SUCCESSOR-2)

Inclusion Criteria \- Participant has documented diagnosis of multiple myeloma and measurable disease, defined as any of the following:. i) Myeloma-protein (M-protein) ≥ 0.5 grams/deciliter (g/dL) by serum protein electrophoresis (sPEP), or. ii) M-protein ≥ 200 milligrams (mg)/24-hour urine collection by urine protein electrophoresis (uPEP) or,. iii) For participants without measurable disease in sPEP or uPEP: serum free light chain levels \> 100 mg/liter (L) (10 mg/dL) involved light chain and an abnormal κ/λ free light chain ratio. * Participant has received at least one prior line of anti-myeloma therapy. Note: One line can contain several phases (e.g., induction, \[with or without\] hematopoietic stem cell transplant, (with or without) consolidation, and/or \[with or without\] maintenance therapy). * Participant must have received prior treatment with lenalidomide and at least 2 cycles of an anti-CD38 monoclonal antibody (mAb) (participants who were intolerant of an anti-CD38 mAb and received \< 2 cycles are still eligible). * Participant achieved minimal response or better to at least 1 prior anti-myeloma therapy. * Participant must have documented disease progression during or after their last antimyeloma regimen. Exclusion Criteria * Participant who has had prior treatment with mezigdomide or carfilzomib. * Participant has previously received allogeneic stem cell transplant at any time or received autologous stem cell transplant within 12 weeks of initiating study treatment. * Other protocol-defined Inclusion/Exclusion criteria apply.