Developments and validation of the FlashSim end-to-end simulation on Run 3 samples

FlashSim is a machine-learning based end-to-end simulation developed in the CMS Collaboration, producing analysis objects in the compact NanoAOD data format directly from the generator-level event record. This note presents the developments of the current version, which targets the Run 3 NanoAOD (version 15) content: the simulation of trigger objects, filter bits and high-level trigger (HLT) decisions, fake objects for jets, muons, electrons, photons and hadronic taus, distilled models running at a few integration steps, a faster input and output stage writing standard NanoAOD files, and modelling improvements across the chain. These developments are validated against the Geant4-based full simulation and reconstruction (FullSim) and the fast parametric simulation (FastSim) on common Run 3 samples, from single-object performance to complete analysis-style selections, together with throughput.