Units of radii for EllipsoidGraphics

When setting the radii property of an EllipsoidGraphics object, it uses a Cartesian3 object. Are those x, y, z values in meters or something else? I understand with EllipseGraphics semiMajor and semiMinor axes are in meters but I was confused by the use of the Cartesian3 to store radius values for the ellipsoid and wanted to clarify.