Status of the LIGO, Virgo, and KAGRA gravitational-wave detectors

The advanced LIGO (Laser Interferometer Gravitational-wave Observatory) detectors are undergoing preparations for the fourth observing run (O4). aLIGO has an ambitious target sensitivity range for O4: 165-190 Mpc for binary neutron star inspirals, an increase from ~120 Mpc in the previous observing run. In this talk I will present the latest status of the aLIGO, adVirgo and KAGRA instruments in the lead up to O4. Focusing on the LIGO detectors, I will cover recent hardware upgrades to the interferometers, including a filter cavity for squeezed light rotation, active mode matching optics, laser amplifier improvements, and test mass replacements. I will discuss commissioning activities and provide a breakdown of the current noise limitations.