Inclusion Criteria:
* Age ≥18 years on the day the Informed Consent Form is signed.
* Histologically or cytologically confirmed R or M HNSCC. Eligible primary tumor locations are oral cavity, hypopharynx, larynx or oropharynx (with documented HPV-negative disease if presenting with OPSCC). Note: primary tumor location of paranasal sinuses and nasopharynx, any histology are excluded.
* No prior systemic therapy administered in the R or M setting; and completed systemic therapy \>6 months prior if given as part of multimodal treatment for locoregionally advanced disease in the adjuvant or definitive setting.
* Archival tumor tissue or willing to undergo pretreatment biopsy at Screening if archival tissue is insufficient or unavailable.
* PD-L1 CPS ≥1.
* Measurable disease based on RECIST 1.1.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Adequate organ function, as defined in the protocol.
Exclusion Criteria:
* Disease suitable for local therapy administered with curative intent.
* Prior treatment with anti-TGFβ therapy.
* Prior therapy with an anti-EGFR antibody (exception: radio sensitizing agents and multimodal treatment for locoregionally advanced disease).
* Prior history of Grade ≥2 intolerance or hypersensitivity reaction to anti-EGFR therapy or other murine proteins.
* Prior therapy with an immune checkpoint inhibitor completed within 6 months prior to study treatment initiation.
* Progressive disease \<6 months from completion of curative intent systemic therapy for locoregionally advanced HNSCC.
* Life expectancy less than 3 months.
* Known active central nervous system metastases, history of spinal cord compression from tumor involvement, a history of carcinomatous meningitis, or leptomeningeal disease are excluded.
* Current active major bleeding, or a recent major bleeding episode within 4 weeks prior to enrollment.
* Subject participated in another clinical study or received treatment with another investigational drug must wait at least 5 half-lives of the treatment received or 4 weeks (whichever is shorter) following prior therapy.
* Active autoimmune disease requiring systemic treatment in the past 2 years.
* Subjects with chronic hepatitis B virus (HBV) infection with active disease who meet the criteria for anti-HBV therapy and are not on a suppressive antiviral therapy prior to initiation of study treatment.
* Subjects with a known history of hepatitis C virus (HCV) who have not completed curative antiviral treatment or have an HCV viral load above the limit of quantification at Screening.
* Known history of human immunodeficiency virus (HIV).
* Receipt of any organ transplantation, including autologous and allogeneic stem cell transplantation, with the exception of transplants that do not require immunosuppression.
* Known to be diagnosed and/or treated for any other additional malignancy within 2 years prior to randomization with the exception of the following: curatively treated basal cell carcinoma or squamous cell carcinoma of the skin, and curatively resected in situ cervical cancer, and curatively resected in situ breast cancer, and low-risk early stage prostate cancer.
* Any condition requiring systemic treatment with either corticosteroids (\>10 mg daily of prednisone or equivalent) or other immunosuppressive medication within 7 days prior to the first dose of study treatment, except for topical, intranasal, intrabronchial, or ocular steroids.
* Use of a live or live attenuated vaccine within 4 weeks prior to Screening.
