Inclusion Criteria:

• Previously untreated participants with CD20-positive LBCL
• Ability to provide tumor tissue
• International prognostic index (IPI) score 2-5
• Eastern cooperative oncology group (ECOG) performance status of 0, 1, or 2
• At least one bi-dimensionally measurable lesion, defined as > 1.5 cm in its longest dimension as measured by CT or MRI
• Left ventricular ejection fraction (LVEF) >/=50% on cardiac multiple-gated acquisition (MUGA) scan or cardiac echocardiogram (ECHO)
• Adequate hematologic function
• Negative HIV test at screening with exceptions as defined by the protocol
• Negative SARS-CoV-2 antigen or PCR test

Exclusion Criteria:

• Contraindication to any of the individual components of Pola-R-CHP or glofitamab, including prior receipt of anthracyclines, or history of severe allergic or anaphylactic reactions to humanized or murine monoclonal antibodies, or known sensitivity or allergy to murine products
• Prior solid organ transplantation
• Current Grade > 1 peripheral neuropathy by clinical examination or demyelinating form of Charcot-Marie-Tooth disease
• History of indolent lymphoma (e.g., Follicular Lymphoma, Marginal Zone Lymphoma, Waldenstrom macroglobulinemia)
• Current diagnosis of the following: Follicular lymphoma grade 3B; transformations of indolent B-cell lymphomas (e.g., de novo transformed follicular lymphoma); mediastinal grey zone lymphoma; primary mediastinal (thymic) large B-cell lymphoma; Burkitt lymphoma; primary large B-cell lymphoma of immune-privileged sites (encompassing primary diffuse large B-cell lymphoma of the CNS, primary large B-cell lymphoma of the vitreoretina and primary large B-cell lymphoma of the testis); primary effusion DLBCL; and primary cutaneous DLBCL, leg type
• Prior treatment with systemic immunotherapeutic agents
• Prior use of any monoclonal antibody for the purposes of treating cancer within 3 months of the start of Cycle 1
• Any investigational therapy for the purposes of treating cancer within 28 days prior to the start of Cycle 1
• Prior radiotherapy to the mediastinal/pericardial region
• Prior therapy for LBCL, with the exception of corticosteriods
• Corticosteroid use > 50 mg/day of prednisone or equivalent, for purposes other than lymphoma symptom control
• History of other malignancy that could affect compliance with the protocol or interpretation of results
• Significant or extensive history of cardiovascular disease
• Recent major surgery (within 4 weeks prior to the start of Cycle 1), other than for diagnosis
• Current or past history of central nervous system (CNS) disease, such as stroke, epilepsy, CNS vasculitis, or neurodegenerative disease
• History of treatment-emergent immune-related adverse events associated with prior immunotherapeutic agents
• Active autoimmune disease which is not well controlled by therapy
• Clinically significant liver disease
• Live, attenuated vaccine within 4 weeks before study treatment infusion on Day 1 of Cycle 1 or anticipation that such a live, attenuated vaccine will be required during the study. Live vaccines during the study and until participants B cells recover are prohibited
• Any active infection within 7 days prior to Cycle 1 Day 1 that would impact participant safety
• Suspected active or latent tuberculosis
• Positive test results for chronic hepatitis B infection, hepatitis C, or the human T-lymphotropic virus type 1 (HTLV-1)
• History of progressive multifocal leukoencephalopathy