The 2012 landmark discovery of the Higgs boson by the ATLAS and CMS experiments marked the beginning of the new era for the LHC to precisely characterise this particle to validate and push the boundaries of the Standard Model through exploration at the highest available energies. To fully exploit the scientific potential of the LHC, both the accelerator and its detectors are undergoing extensive upgrades as part of the High-Luminosity LHC (HL-LHC) project, corresponding to an expected number of 140 to 200 simultaneous proton–proton interactions per bunch crossing by the end of the decade. A central element of this effort is the reinforcement of the forward muon system, for which CMS is deploying three new GEM-based muon stations: GE1/1, GE2/1, and ME0. These detectors combine excellent spatial resolution (∼250 μm), high-rate capability (>1 kHz/cm²), and radiation tolerance, while providing additional coordinate measurements and redundancy in combination with the existing Cathode Strip Chambers (CSCs) and RPCs. The GE1/1 station consists of 144 triple-GEM modules, arranged in super-chambers in both CMS endcaps, covering the range 1.55 < ∣η∣ < 2.18. The GE2/1 station, with 72 GEM chambers composed of 288 modules, extends coverage approximately over 1.62 < ∣η∣ < 2.43. The six-layer ME0 station, covering approximately 60 m², will be installed behind the new high-granularity calorimeter (HGCAL) during the third Long Shutdown (LS3) and will extend the CMS muon system’s pseudo-rapidity coverage from |η| < 2.4 to |η| < 2.8. Full system of GE1/1 and a few GE2/1 stations are contributing to the data taking in Run-3 with an operational efficiency above 95%. GEM technology efficiently rejects background and improves the precision of the muon bending angle measurement. This work presents an overview of the muon spectrometer upgrade of the CMS with GEM detectors, including operational experience and performance of the GEM station.