WGS 84 + EGM2008 height - EPSG:9518

WKT

HVCOORDSYS["WGS_1984_and_EGM2008_height", 
	GEOGCS["GCS_WGS_1984", 
		DATUM["D_WGS_1984", 
			SPHEROID["WGS_1984", 6378137.0, 298.257223563]], 
		PRIMEM["Greenwich", 0.0], 
		UNIT["Degree", 0.0174532925199433]], 
	VERTCS["EGM2008_height", 
		VDATUM["EGM2008_Geoid"], 
		PARAMETER["Vertical_Shift", 0.0], 
		PARAMETER["Direction", 1.0], 
		UNIT["Meter", 1.0]]]

WKT2

COMPOUNDCRS["WGS_1984_and_EGM2008_height", 
	GEOGCRS["GCS_WGS_1984", 
		DYNAMIC[
			FRAMEEPOCH[1990.5], 
			MODEL["AM0-2"]], 
		DATUM["D_WGS_1984", 
			ELLIPSOID["WGS_1984", 6378137.0, 298.257223563]], 
		PRIMEM["Greenwich", 0.0], 
		CS[ellipsoidal, 2], 
		AXIS["Latitude (lat)", north, 
			ORDER[1]], 
		AXIS["Longitude (lon)", east, 
			ORDER[2]], 
		ANGLEUNIT["Degree", 0.0174532925199433]], 
	VERTCRS["EGM2008_height", 
		VDATUM["EGM2008_Geoid"], 
		CS[vertical, 1], 
		AXIS["Gravity-related height (H)", up, 
			LENGTHUNIT["Meter", 1.0]]], 
	ID["EPSG", "9518"]]

Data from @esri/proj-codes

{
  "wkid": 9518,
  "latestWkid": 9518,
  "pcsWkid": 0,
  "gcsWkid": 4326,
  "vcsWkid": 3855,
  "macro": "PE_HVC_WGS_84_EGM2008_HEIGHT",
  "name": "WGS_1984_and_EGM2008_height",
  "wkt": "HVCOORDSYS[\"WGS_1984_and_EGM2008_height\",GEOGCS[\"GCS_WGS_1984\",DATUM[\"D_WGS_1984\",SPHEROID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],VERTCS[\"EGM2008_height\",VDATUM[\"EGM2008_Geoid\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]]",
  "wkt2": "COMPOUNDCRS[\"WGS_1984_and_EGM2008_height\",GEOGCRS[\"GCS_WGS_1984\",DYNAMIC[FRAMEEPOCH[1990.5],MODEL[\"AM0-2\"]],DATUM[\"D_WGS_1984\",ELLIPSOID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433]],VERTCRS[\"EGM2008_height\",VDATUM[\"EGM2008_Geoid\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]]],ID[\"EPSG\",\"9518\"]]",
  "description": "WGS 84 + EGM2008 height",
  "authority": "EPSG",
  "version": "10.013(13.2.0)",
  "deprecated": "no",
  "areaname": "World",
  "extent": {
    "slat": -90,
    "nlat": 90,
    "llon": -180,
    "rlon": 180
  }
}