Fixed Duration Pirtobrutinib and Obinutuzumab in Chronic Lymphocytic Leukemia

Key Inclusion Criteria: * Meet 2018 International Workshop on Chronic Lymphocytic Leukemia (IWCLL) guidelines for the diagnosis of chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). * Presence of measurable disease (absolute lymphocyte count \> 5,000/µL, palpable or measurable lymph nodes ≥1.5cm on imaging, or bone marrow involvement of CLL ≥ 30%). * No prior systemic therapy for CLL or SLL. * Currently have an indication for treatment as defined by the following 2018 IWCLL guidelines * Age ≥ 18 years * Eastern Cooperative Oncology Group performance status ≤ 2 * Adequate organ and bone marrow function as defined by the study protocol * Ability to take oral medications. * Ability to understand and the willingness to sign a written informed consent document. Key Exclusion Criteria: * Known or suspected Richter's transformation or known central nervous system involvement. * History of bleeding disorders * History of stroke or intracranial hemorrhage within 6 months of starting study therapy. * Significant cardiovascular disease such as uncontrolled arrhythmia, Class 3 or 4 congestive heart failure as defined by the New York Heart Association Functional Classification, or left ventricular ejection fraction \< 40% by any methods in the 12 months prior to study therapy. * History of other malignancies with life expectancy of \< 2 years. * Receiving any other investigational agents. * Concurrent systemic immunosuppression \< 28 days of study therapy or administration of \> 20 mg of prednisone or equivalent daily \< 7 days of study therapy. * Vaccinated with live vaccine within 4 weeks of starting study therapy. * Major surgery within 4 weeks of starting study therapy. * Ongoing or recent infection requiring intravenous antimicrobials at time of screening. Prophylactic antibiotics are allowed if there is no evidence of active infection and the antibiotics is not included on the list of the prohibited medications. * Patients who have tested positive for HIV are excluded due to potential drug-drug interactions between anti-retroviral medications and pirtobrutinib and risk of opportunistic infections with both HIV and irreversible BTK inhibitors. For patients with unknown HIV status, HIV testing will be performed at Screening and result should be negative for enrollment. * Active human T cell leukemia virus infection or active hepatitis B or C virus infection * Known active cytomegalovirus infection * Pregnancy, lactation or plan to breastfeed during the study or within 6 months of the last dose of study treatment. * Clinically significant active malabsorption syndrome or other condition likely to affect gastrointestinal absorption of the study drug * Active uncontrolled auto-immune cytopenia. * Significant co-morbid condition or disease.