Participants with unresectable, locally advanced recurrent or metastatic ESCC who have
        Stage IV unresectable ESCC at first diagnosis (ie, Stage IV disease at the original
        diagnosis of ESCC) or who have unresectable, locally advanced recurrent or metastatic
        disease with at least a 6-month treatment-free interval, if prior definitive therapy
        (chemotherapy, chemo-radiation therapy or surgery) was given.

        Key Inclusion Criteria:

          1. Pathologically (histologically) confirmed diagnosis of ESCC

          2. Stage IV unresectable ESCC at first diagnosis OR unresectable, locally advanced
             recurrent or metastatic disease with a treatment free interval of at least 6 months
             after definitive treatment.

        Key Exclusion Criteria:

          1. Palliative radiation treatment for ESCC within 4 weeks of study treatment initiation

          2. Prior systemic therapy for unresectable, locally advanced recurrent or metastatic ESCC

          3. Received prior therapies targeting programmed cell death protein-1 (PD-1), programmed
             cell death protein ligand-1 (PD-L1) or PD-L2

          4. Participants with evidence of fistula (either esophageal/bronchial or
             esophageal/aorta)

          5. Uncontrollable pleural effusion, pericardial effusion, or ascites requiring frequent
             drainage or medical intervention (clinically significant recurrence requiring an
             additional intervention within 2 weeks of intervention)

          6. Evidence of complete esophageal obstruction not amenable to treatment

          7. Unintentional weight loss ≥ 5% within one month prior to randomization or Nutritional
             Risk Index (NRI) < 83.5 per investigator's choice

          8. Locally advanced esophageal carcinoma that is resectable or potentially curable with
             radiation therapy per local investigator.

          9. Participants with untreated chronic hepatitis B or chronic hepatitis B virus (HBV)
             carriers whose HBV DNA is ≥ 500 IU/mL or participants with active hepatitis C virus
             (HCV)

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