The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics, and activity of XmAb24306 in combination with cevostamab in participants with relapsed/refractory multiple myeloma (R/R MM) who have received a minimum of three prior treatments, including at least one immunomodulatory drug (IMiD), one proteasome inhibitor (PI), and one anti-CD38 monoclonal antibody.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Life expectancy of at least 12 weeks
• Participants must have received a minimum of 3 prior lines of therapy, including at least one PI, one IMiD, and an anti-CD38 monoclonal antibody.
• Documented evidence of progressive disease on or after the last prior therapy, or participants who were intolerant to the last prior therapy.
• Measurable disease, as defined by the protocol
• Participants agree to follow contraception or abstinence requirements as defined in the protocol

Exclusion Criteria:

• Any anti-cancer therapy within 3 weeks prior to initiation of study treatment with exception defined by the protocol
• Participants with autologous stem cell transplantation (SCT) within 100 days prior to first dose of study treatment
• Participants with prior allogeneic SCT or solid organ transplantation
• Known history of hemophagocytic lymphohistiocytosis (HLH) or macrophage activation syndrome (MAS)
• Active or history of autoimmune disease
• Participants with current or history of Central Nervous System (CNS) disease, or current CNS involvement by Multiple Myeloma (MM)
• Significant cardiovascular disease
• Participants with known clinically significant liver disease
• Symptomatic active pulmonary disease requiring supplemental oxygen
• Known active infection requiring intravenous anti-microbial therapy within 14 days prior to first study drug administration
• Any episode of active, symptomatic COVID-19 infection, or requiring treatment with IV antivirals for COVID-19 (not including COVID-19 primary prophylaxis) within 14 days, prior to first study treatment
• Other protocol defined inclusion/exclusion criteria may apply

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing