X-PET is a commercial small animal PET scanner incorporating several innovative designs to achieve improved performance. It is employed as a PET subsystem in the FLEX Triumph preclinical PET/CT scanner, the first commercial small animal PET/CT scanner worldwide. The authors report on a novel Monte Carlo (MC) model designed for the evaluation of performance parameters of the X-PET METHODS: The Geant4 Application for Tomographic Emission (GATE) MC code was used as a simulation tool. The authors implemented more accurate modeling of the geometry of detector blocks and associated electronic chains, including dead-time and time-independent parameters, compared to previously presented MC models of the X-PET scanner. Validation of the MC model involved comparison between simulated and measured performance parameters of the X-PET, including spatial resolution, sensitivity, and noise equivalent count rate (NECR). Thereafter, various simulations were performed to assess scanner performance parameters according to NEMA NU 4-2008 standards with the aim to present a reliable Monte Carlo platform for small animal PET scanner design optimization.