The COmpact DEtector for EXotics at LHCb (CODEX-b) is a particle physics detector proposal dedicated to searching for displaced decays of exotic long-lived particles (LLPs), compelling signatures of dark sectors beyond the Standard Model, which arise in theories containing a hierarchy of scales and small parameters. CODEX-b is planned to be installed near the LHCb interaction point at the LHC, it comprises the use of fast RPCs and, because of the location, an almost-zero background environment to complement the program of New Physics searches of other detectors like ATLAS or CMS. A demonstrator detector, CODEX-$\beta$, is being assembled now to take data beginning in the 2025. It will validate the design and physics case for the future CODEX-b. CODEX-$\beta$ will be responsible for validating the background estimations for CODEX-b, demonstrating the seamless integration in the LHCb readout system and the suitability of RPC’s as standalone tracking detectors.