Near-term Upgrades for the Advanced LIGO, Advanced Virgo, and KAGRA Gravitational-wave Detectors

The Advanced LIGO, Advanced Virgo, and KAGRA detectors have continued to expand the reach of gravitational-wave astronomy, enabling precision observations of compact binary mergers and providing unprecedented constraints on fundamental physics and astrophysics. The global network completed its fourth observing run (O4) in November 2025, achieving the highest duty factors and broadband sensitivities to date. During O4, the detectors operated with upgraded laser, suspension, and quantum-noise–reduction technologies that substantially increased the astrophysical event rate relative to previous runs. I will begin with an overview of instrument performance during O4 and then focus on several key challenges encountered across the sites, including noise sources that limited low-frequency sensitivity, issues affecting detector duty cycle and stability, and lessons learned from commissioning efforts throughout the run. I will then discuss the suite of upgrades being implemented during the current commissioning period in preparation for the next observation run.