Many beyond-the-standard model theories propose the existence of new ‘long-lived’ particles (LLPs) with macroscopic decay lengths that may be produced in high energy collisions at the LHC. While extensive searches for LLPs have been performed by existing LHC experiments such as ATLAS, CMS, and LHCb, their sensitivity to very long-lived models (ct>~10 m) is constrained by the physical size of the detectors. The proposed ANUBIS experiment is designed to significantly extend experimental sensitivity to these very long-lived models by instrumenting the ceiling of the ATLAS detector cavern with RPC detectors. In addition to extending the decay volume, the transverse positioning provides sensitivity to LLP models with high-mass mediators, complementing the sensitivity of existing forward detectors to lower-mass models. In this talk, the physics case for ANUBIS proposal will be presented alongside its expected backgrounds, projected physics reach for several benchmark LLP models, and the latest results from the proANUBIS demonstrator within the ATLAS cavern.