Inclusion Criteria:

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1

          -  Life expectancy of at least 12 weeks

          -  Participants must have relapsed or refractory (R/R) multiple myeloma (MM) for which no
             established therapy for MM is appropriate and available or be intolerant to those
             established therapies

          -  Adverse events from prior anti-cancer therapy resolved to Grade < or = 1, except any
             grade alopecia and/or peripheral sensory or motor neuropathy which must have resolved
             to Grade < or = 2

          -  Measurable disease defined by laboratory test results

          -  Female participants of childbearing age must agree to remain abstinent or use reliable
             contraceptive methods during the treatment period, and at least 3 months after last
             dose of study drug

          -  Male participants must agree to refrain from donating sperm, to abstain or use a
             condom during the treatment period, and at least 60 days after last dose of study drug

        Exclusion Criteria:

          -  Inability to comply with protocol-mandated hospitalization and activities restrictions

          -  Pregnant, lactating, or planning to become pregnant during the study and up to 3
             months after last dose of study drug

          -  Prior use of any monoclonal antibody, radioimmunoconjugate, or antibody-drug conjugate
             as anti-cancer therapy within 4 weeks before first infusion

          -  Prior treatment with systemic immunotherapeutic agents within 12 weeks or 5 half-lives
             of the drug, whichever is shorter, before first infusion

          -  Prior treatment with chimeric antigen receptor (CAR) T-cell therapy within 12 weeks
             before first cevostamab infusion

          -  Known treatment-related, immune-mediated adverse events associated with prior
             immunotherapeutic agents

          -  Treatment with radiotherapy, any chemotherapeutic agent, or treatment with any other
             anti-cancer agent (investigational or otherwise) within 4 weeks or 5 half-lives of the
             drug, whichever is shorter, prior to first cevostamab infusion

          -  Autologous stem cell transplantation (SCT) within 100 days prior to first infusion

          -  Prior allogeneic SCT or solid organ transplantation

          -  Absolute plasma cell count exceeding 500/micro L or 5% of the peripheral blood white
             cells

          -  History of autoimmune disease or of confirmed progressive multifocal
             leukoencephalopathy

          -  History of severe allergic or anaphylactic reactions to monoclonal antibody therapy
             (or recombinant antibody-related fusion proteins)

          -  Patients with known history of amyloidosis (e.g., positive Congo Red stain or
             equivalent in tissue biopsy)

          -  Patients with lesions in proximity of vital organs that may develop sudden
             decompensation/deterioration in the setting of a tumor flare

          -  History of other malignancy that could affect compliance with the protocol or
             interpretation of results

          -  Current or past history of central nervous system (CNS) disease, or CNS involvement by
             MM

          -  Significant cardiovascular disease that may limit a patient's ability to adequately
             respond to a CRS event

          -  Symptomatic active pulmonary disease requiring supplemental oxygen

          -  Within 14 days prior to first cevostamab infusion: known active bacterial, viral,
             fungal, mycobacterial, parasitic, or other infection (excluding fungal infections of
             nail beds) at study enrollment, or any major episode of infection requiring treatment
             with IV antibiotics within 4 weeks prior to first infusion

          -  Known or suspected chronic active Epstein-Barr virus (EBV) infection, acute or chronic
             hepatitis C virus (HCV) infection

          -  Positive serologic or polymerase chain reaction (PCR) test results for acute or
             chronic hepatitis B virus (HBV) infection

          -  Recent major surgery within 4 weeks prior to first infusion

          -  Human Immunodeficiency Virus (HIV) positive

          -  History of illicit drug or alcohol abuse within 12 months prior to screening

          -  Any medical condition or laboratory test abnormality that precludes the participant's
             safe participation in and completion of the study, or which could affect compliance
             with the protocol or interpretation of results