We give an overview of the official Athena WFI instrument simulator implemented in the SIXTE end-to-end simulation toolkit. From a description of any astrophysical source, SIXTE simulates the entire detection pipeline of the Athena WFI to the final data product. The source description can consist of point sources and extended sources, including sources with spatially and temporally variable spectra and deep X-ray fields with thousands to millions of sources. The simulator aims to provide a

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... sentative model for the imaging and spectroscopic performance of the WFI to study and optimize the instrument's capabilities and scientific potential. The setup includes the essential detector and readout effects specific to the WFI DEPFET sensors, such as pile-up and charge cloud splitting. As an application, we present the WFI performance during observations of very bright sources where high incident photon rates can degrade the overall instrument performance.