A Window of Opportunity Trial to Learn if Linvoseltamab is Safe and Well Tolerated, and How Well it Works in Adult Participants With Recently Diagnosed Multiple Myeloma Who Have Not Already Received Treatment

This study is researching an experimental drug called linvoseltamab (called "study drug"). The study is focused on participants with newly diagnosed multiple myeloma (NDMM) who are eligible for high dose chemotherapy with autologous stem cell transplantation (transplant-eligible) or ineligible for autologous stem cell transplantation (transplant-ineligible). The aim of this clinical trial is to study the safety, tolerability (how the body reacts to the drug), and effectiveness (tumor shrinkage) of linvoseltamab in study participants with NDMM as a first step in determining if the study drug has a role in the treatment of NDMM. This study consists of 2 phases: * In Phase 1 Parts A and B, the study drug will be given to participants to study the side effects of the study drug and to establish the regimen (initial doses and full dose) of the study drug to be given to participants in Phase 2. * In Phase 1 Part C, the study drug will be given to participants to study the side effects when using different initial doses of the study drug. * In Phase 2, the study drug will be given to more participants to continue to assess the side effects of the study drug and to evaluate the activity of the study drug to shrink the tumor (multiple myeloma) in participants with NDMM. The study is looking at several research questions, including: * What side effects may happen from taking linvoseltamab? * What the right dosing regimen is for linvoseltamab? * How many participants treated with linvoseltamab have improvement of their disease and for how long? * The effects of linvoseltamab study treatment before and after transplant * How much linvoseltamab is in the blood at different times? * Whether the body makes antibodies against linvoseltamab (which could make the drug less effective or could lead to side effects).