The MilliQan Experiment Upgrade in Run 3

The MilliQan Experiment, located at the Large Hadron Collider near CMS, searches for millicharged particles (mCP), which arise naturally in dark sector models. The experiments consist of two detectors: the bar detector with long scintillating bars to provide sensitivity to low-charge mCPs, which has been collecting LHC Run 3 data since June 2023 and has accumulated 140 fb^-1 data, and the slab detector with wide scintillating slabs to provide larger geometric acceptance for higher-mass models. This presentation focuses on the recently assembled slab detector, including the construction, initial commissioning results, and detector performance. In addition, the initial results of a new system that provides broad calibration and testing with in-situ LED pulsing offer new insight into the detectors.