The main inclusion criteria include but are not limited to the following: - Has a histologically confirmed diagnosis of locally advanced unresectable or metastatic (unresectable Stage III or Stage IV as defined by American Joint Committee on Cancer [AJCC] eighth edition) colorectal adenocarcinoma - Part 2 only: Has not received systemic anticancer therapy for locally advanced unresectable or metastatic colorectal cancer - Tumor tissue demonstrates presence of a Kirsten rat sarcoma viral oncogene homolog G12C (KRAS G12C) mutation - Human immunodeficiency virus (HIV)-infected participants must have well controlled HIV on antiretroviral therapy (ART) - Participants who are Hepatitis B surface antigen (HBsAg) positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy and have undetectable HBV viral load - Participants with history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable

The main exclusion criteria include but are not limited to the following: - Has active inflammatory bowel disease requiring immunosuppressive medication or previous clear history of inflammatory bowel disease (eg, Crohn's disease, ulcerative colitis, chronic diarrhea) - Has uncontrolled, significant cardiovascular disease or cerebrovascular disease - Has known dihydropyrimidine dehydrogenase (DPD) deficiency - HIV-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease - Has received prior systemic anticancer therapy including investigational agents within 4 weeks before randomization - Has 1 or more conditions that, in the opinion of the investigator, make the participant ineligible for treatment with bevacizumab - Has known additional malignancy that is progressing or has required active treatment within the past 3 years - Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis or leptomeningeal disease - Has active infection requiring systemic therapy - Has not adequately recovered from major surgery or have ongoing surgical complications - Has a history of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease