Primary Objective:~1. Estimate the therapeutic activity (undetectable measurable residual disease [U-MRD] rate) of combined pirtobrutinib, venetoclax, and obinutuzumab in patients with previously untreated CLL/SLL (cohort 1) by undetectable measurable residual disease (U-MRD) rate and Richter transformation (cohort 2) by overall response rate (ORR) (defined as CMR//PMR).~Secondary Objectives:~To estimate the therapeutic activity of combination therapy by determining:~Combined response rate (defined as CR/CRi/PR) as assessed by the investigator for cohort 1 (CLL/SLL)~Progression free survival (PFS) and overall survival (OS).~U-MRD response with next generation sequencing assay for cohort 2~To determine the safety and tolerability of this combination therapy~Exploratory Objective:~To study immunological and molecular changes in the peripheral blood and bone marrow in response to pirtobrutinib, venetoclax, and obinutuzumab.~To evaluate the kinetics of MRD response over time
To learn if the combination of pirtobrutinib (also called LOXO-305), venetoclax, and obinutuzumab is safe and effective when given to patients with chronic lymphocytic leukemia (CLL) or Richter transformation (RT) who have not previously received treatment.