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:

1. Myeloma-protein (M-protein) ≥ 0.5 grams/deciliter (g/dL) by serum protein electrophoresis (sPEP), or
2. M-protein ≥ 200 milligrams (mg)/24-hour urine collection by urine protein electrophoresis (uPEP) or,
3. 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 .
4. 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).
5. 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).
6. Participant achieved minimal response or better to at least 1 prior anti-myeloma therapy.
7. Participant must have documented disease progression during or after their last antimyeloma regimen.

Exclusion Criteria:

1. Participant who has had prior treatment with mezigdomide or carfilzomib.
2. Participant has previously received allogeneic stem cell transplant at any time or received autologous stem cell transplant within 12 weeks of initiating study treatment.

Additional protocol-defined criteria apply.