The Schubert polynomials and key polynomials form two important bases for the polynomial ring. Schubert and key polynomials are the​``bottom layers” of Grothendieck and Lascoux polynomials, two inhomogeneous polynomials. In this talk, we look at their​``top layers”. We develop a diagrammatic way to compute the degrees and the leading monomials of these top layers. Finally, we describe the Hilbert series of the space spanned by these top layers, involving a classical $q$-analogue of the Bell numbers.