An implant assembly including an expandable vertebral body replacement implant. Two outer cores disposed on opposing ends of an inner are configured to move away from each other when the inner core is actuated. The implant assembly may include removable endplate configured to engage vertebral bodies as interbody spacer or through a corpectomy. The implant may include a locking mechanism to prevent collapse or movement the implant assembly after implantation. The locking mechanism may be automatically engage after removal of an inserter instrument from the implant assembly.