The primary purpose of the study is to characterize the safety and tolerability of XB371. The dose-escalation cohorts and Part B of the expansion cohorts are non-randomized. Part A of the expansion cohorts is randomized.

Key Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.
• Minimum life expectancy of ≥ 12 weeks.
• Recurrent locally advanced or metastatic solid tumors.
• Adequate end organ and bone marrow function.

Key Exclusion Criteria:

• Primary brain tumors or known active brain metastases, leptomeningeal, or cranial epidural disease.
• History of interstitial lung disease (ILD) of any grade or history of organizing pneumonia.
• Has acute ocular infection, acute or chronic ulcerative/cicatricial condition of conjunctiva or cornea.
• Known history of immunodeficiency virus (HIV) unless specific criteria are met.
• Active infection with hepatitis C virus (HCV) defined as positive for HCV antibody.
• Major surgery within 4 weeks before the first dose of study treatment.
• Received radiation therapy within 2 weeks before the first dose of study treatment.
• Received prior systemic anticancer therapy including investigational agents within 4 weeks before the first dose of study treatment.

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