Venetoclax is a standard treatment for patients with CLL following covalent BTK inhibitor (cBTKi) therapy, despite relatively limited prospective data in this setting. Pirtobrutinib is a highly selective, non-covalent (reversible) BTKi that was designed to overcome the pharmacologic limitations of cBTKi and re-establish BTK inhibition. An unanchored matching-adjusted indirect comparison (MAIC) was conducted to estimate the treatment effect of pirtobrutinib versus venetoclax monotherapy in patients with cBTKi pre-treated CLL. Data from patients with CLL who were venetoclax-naïve and pre-treated with cBTKi received pirtobrutinib (n=146) in the phase 1/2 BRUIN study were compared with the only identified trial of patients with CLL receiving venetoclax after a cBTKi (n=91), as administered as monotherapy until progression. Outcomes included progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and treatment-emergent adverse events (TEAEs). Both unweighted and weighted analyses were conducted. PFS and OS of pirtobrutinib and venetoclax were comparable in both unweighted and weighted analyses (weighted hazard ratios for PFS: 1.01, 95% CI: 0.58-1.73, p=0.98 and OS: 0.64, 95% CI: 0.25-1.67, p=0.34). ORR was significantly higher for pirtobrutinib (80.2% vs 64.8%, p=0.01). Grade ≥3 TEAEs were lower in weighted analyses for pirtobrutinib vs venetoclax (all p.