Key Inclusion Criteria:

• Histologically confirmed diagnosis of Stage II or III adenocarcinoma of colon or rectum.
• Documented local MSI and/or mismatch repair (MMR) test result demonstrating MSS, MSI-low, or pMMR status.
• Colon or rectal cancer with completed definitive therapy.
• ctDNA-positive based on local testing using the Natera Signatera tissue-informed molecular residual disease (MRD) assay.
• No radiographic evidence of disease, as confirmed by a negative baseline computed tomography (CT) of the chest, abdomen, and pelvis (CAP), or CT of chest and magnetic resonance imaging (MRI) of abdomen/pelvis.

Key Exclusion Criteria:

• History of solid organ or allogeneic stem cell transplant.
• Known additional malignancy that is progressing or has required active treatment within the past 2 years.
• Prior treatment with immune checkpoint inhibitors (ICIs) or Vascular endothelial growth factor receptor (VEGFR) inhibitors.
• History of CRC requiring systemic anticancer therapy prior to the definitive therapy.
• Use of systemic anticancer therapy (including investigational therapy) or radiation therapy after the completion of definitive therapy.
• Administration of a live, attenuated vaccine within 30 days of randomization and during treatment.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.