The Upgrade of the CMS Electromagnetic Calorimeter for HL-LHC.

The High-Luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of around $5 \times$ 10^$34 {cm^{-2}\,s^{-1}}$ and $3000/{fb}$, respectively. An average of 140 to 200 collisions per bunch-crossing (pileup) is expected. The upgraded ECAL will feature new readout electronics that will greatly improve the time resolution for photons and electrons with energies above $10 {GeV}$. We present the status of the ECAL barrel upgrade, including time resolution results from beam tests conducted during 2018 and 2021 at the CERN SPS.