The Gas Electron Multiplier (GEM) detector upgrades at the CMS experiment

The upcoming high-luminosity upgrades to the LHC will increase the instantaneous luminosity delivered to the experiments, which will allow a significant expansion of its physics program. The expected luminosity exceeds 5 times the original LHC design, requiring the experiments to improve their performance and sustain higher particle fluxes, and the detectors in the forward regions are the most affected. In the muon detector system of the CMS experiment, a new station of Gas Electron Multipliers (GEM) has been installed during the last shutdown (GE1/1), and it's being operated during LHC Run-3. Three GE2/1 chambers have additionally been installed during the pauses of the current Run-3, while the rest is postponed to after high luminosity upgrades. The last and most forward GEM station, ME0, is currently in production phase and will be installed in the next long shutdown. This talk will present the operations and the performances of the GEM detectors currently installed in CMS, focusing on the challenges and the successes towards its inclusion in the data taking and in the L1 trigger.