Guided busways (or bus guideways in OSM terminology) are special roadways along which bus operators can travel smoothly at high speeds without steering. These are tagged highway=bus_guideway on OpenStreetMap.
Currently, highway=busway is surfaced in OpenMapTiles as the busway class in the transportation layer, but highway=bus_guideway is not present. These two types of roadways serve generally similar purposes, so it would make sense to have guided busways at the same zoom levels.