In this talk, I'll discuss a new proposal for an extension of the CMS physics program at the HL LHC to look for light long-lived particles (such as ALPs, dark photons and Higgs bosons, Majorana neutrinos) in a FACET detector to be installed about 100 m downstream from the CMS interaction point. I'll discuss the vast physics landscape covered by FACET, a conceptual detector design, andfirst sensitivity studies showing that it has significantly extended sensitivity compared to the existing and proposed competing experiments.