What CRS does GFS use?
My ansatz for what cyl means is likely Equidistant Cylindrical Projection, because in the older Basemap module, 'cyl' was the shortname for that projection.
But the reality is that since the GFS is a global spectral model with a latitude-longitude grid, it likely does not require a CRS. That is, it presupposes a sphere, where a CRS projects the spherical coordinates (latitude, longitude) onto a shape (such as a cone).