A Study Evaluating Safety, Tolerability, and Clinical Activity of Forimtamig-Based Treatment Combinations in Participants With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 Life expectancy of at least 12 weeks Documented diagnosis of MM according to the IMWG diagnostic criteria Evidence of progressive disease based on Investigator's determination of response by IMWG criteria on or after last dosing regimen Measurable disease AEs from prior anti-cancer therapy resolved to Grade ≤ 1, Adequate organ functions Exclusion Criteria: Pregnant or breastfeeding or intending to become pregnant during the study or within 3 months after the last dose of study drug Plasma cell leukemia with circulating plasma cell count ≥ 5% or >500/microliter (µL) Participants with current amyloidosis Participants with myelodysplastic syndrome Prior treatment with monoclonal antibody (mAb) and antibody-drug conjugate within 4 weeks or 5 half-lives of the drug, whichever is shorter Prior anti-cancer therapy (chemotherapy, small molecule/tyrosine kinase inhibitors, radiotherapy) within 14 days prior to first forimtamig administration Prior solid organ transplantation Active auto-immune disease or flare within 6 months prior to start of study treatment Known or suspected chronic active Epstein-Barr virus (EBV) infection Hepatitis B virus (HBV) infection Acute or chronic hepatitis C virus (HCV) infection Known history of HIV seropositivity Live vaccine(s) within one month prior to start of the treatment Participants not fully vaccinated for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as per local recommendations Previous refractoriness to carfilzomib Participants who discontinued prior carfilzomib treatment due to treatment-related toxicity Participants with known liver cirrhosis