The 2025 International Workshop on the High Energy Circular Electron Positron Collider

The High-Luminosity LHC upgrade will present unprecedented challenges, including intense radiation and up to 200 simultaneous proton collisions. To cope with this, the CMS experiment will deploy a new MIP Timing Detector (MTD) to precisely timestamp MIP particles. This contribution focuses on the MTD's Barrel Timing Layer (BTL), which is now transitioning from a successfully validated design to full-scale construction, highlighting its innovative crystal-based technology and assembly progress.