The TAx4 experiment is a project to observe highest energy cosmic rays by expanding the detection area of the Telescope Array (TA) experiment with newly constructed surface detectors (SDs) and fluorescence detectors (FDs). The construction of both SDs and FDs is ongoing. New SDs are arranged in a square grid with 2.08 km spacing at the north east and south east of the TA SD array. Field of view of new FDs overlaps the detection area of new SDs to observe SD FD hybrid events. More than half of the new SDs were deployed on February and March 2019. The first light with new FDs was observed on February 16th, 2018. The performance of the constructed detectors and the prospects of the detector deployment and operation will be shown in this talk as well as proposed physics program. The latter includes high exposure analysis of the hotspot and energy spectrum anisotropy with the extended TA experiment.