Do GUIX and NixOS differ architecturally?

(This is not a "which distribution is better" question!) GNU GUIX and NixOS are two Linux distributions based on the NixOS package manager. I realize that GUIX seems to use Guile for defining packages/dependencies or other meta-data uses; and I'm guess everything in GUIX is GPL'ed, while perhaps not everything in NixOS is... but those seem more like superficial differences. What I'm hoping to understand is whether these two distributions have _architectural_ differences of any significance.