This study consists of a Dose-Escalation stage and a Dose Expansion stage. The primary purpose of the dose escalation stage is to determine the maximum tolerated dose (MTD) and/or recommended dosage(s) for expansion (RDE[s]); and the dose expansion stage is to evaluate the preliminary antitumor activity of XB628 as a single agent and in combination with zanzalintinib.

Key Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.
• Minimum life expectancy of ≥ 12 weeks.
• Have a recurrent advanced or metastatic solid tumor that is histologically or cytologically confirmed.
• Adequate organ and marrow function.
• Not amenable to curative treatment with surgery or radiation.
• Received at least 1 line of prior systemic anticancer therapy in the recurrent or metastatic setting.
• Acceptable alternative therapy was received, refused, intolerable, or no longer effective.
• Capable of understanding and complying with the protocol requirements and provide signed informed consent according to the protocol and local requirements.

Key Exclusion Criteria

• Primary brain tumors or known active brain metastases.
• Major surgery (eg, gastrointestinal surgery, removal or biopsy of brain metastasis) within 4 weeks before the first dose of study treatment.
• Received radiation therapy within 1 week before the first dose of study treatment or clinically relevant ongoing complications from prior radiation therapy.
• Received prior therapy targeting NK cells (eg, monalizumab).
• A woman of childbearing potential has a positive serum pregnancy test within 7 days prior to study treatment.

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