• Diagnosed with MM per International Myeloma Working Group (IMWG) criteria

• Eastern Cooperative Oncology Group Performance Status of 0, or 1, or 2

• Resolution of AEs from prior anti-cancer therapy to Grade \<=1

• Agreement to undergo scheduled assessments and procedures

⁃ Additional Inclusion Criteria for SS2:

• Completion of planned induction therapy and achievement of at least a partial response (PR)

• Autologous Stem Cell Transplant (SCT) within 100 days prior to first study treatment and the absence of progressive disease

• Cytogenetic high-risk features at diagnosis

• Treatment with any investigational medicinal products, systemic cancer therapies, immunotherapies received previously in CO43923 (any arms) within 5 half-lives or 3 weeks whichever is the shortest

• Agreement to comply with all local requirements of the lenalidomide risk minimization plan, which includes the global pregnancy prevention program

• For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraception

• For male participants: agreement to remain abstinent (refrain from heterosexual intercourse) or use a condom even if they have had a prior vasectomy, and agreement to refrain from donating sperm

⁃ Additional Inclusion Criteria for SS4:

• Previously exposed to at least a PI, an IMiD, and an anti-CD38 antibody for the treatment of R/R MM for whom no suitable SOC therapy options are available