Inclusion Criteria:  Relapsed/refractory multiple myeloma with at least 3 prior lines of therapy Refractory to at least one IMiD, one proteasome inhibitor, and one anti-CD38 antibody  Measurable disease defined by at least one of the following:  Serum M-protein >/= 0.5 g/dL by SPEP Urinary M-protein excretion >/= 200 mg/24 hours by UPEP Serum immunoglobulin FLC >/= 10 mg/dL (>/= 100 mg/L) AND abnormal serum immunoglobulin kappa to lambda FLC ratio ECOG performance status 0 -1 Resolved acute effects of any prior therapy to baseline severity or CTCAE Grade </= 1  Exclusion Criteria:  Active plasma cell leukemia Amyloidosis Stem cell transplant with 12 weeks prior to enrollment, or active GVHD POEMS syndrome Any active uncontrolled bacterial, fungal, or viral infection Impaired cardiovascular function or clinically significant cardiovascular diseases within 6 months prior to enrollment Previous treatment with an anti-BCMA bispecific antibody Previous administration with an investigational drug within 30 days or 5 half-lives preceding the first dose of study treatment (whichever is longer)