I haven't tried it in almost a year, but using Claude Code for setting up my nix config back then worked amazingly well. I've only dabbled in NixOS, and I'm very tempted to it for my workstation when I reinstall it in the next month.
Given how much Claude Code + Opus have improved in the last year, I'd give it a fighting chance to make a nice Nix config. I'll probably start setting up a spare laptop to get the base configs dialed in before switching over to it.
Using AI to generate Nix config is a superpower. Because the entire system is declared in a single set of config, you can basically spell cast any system you want. I one-shotted a Linux distro with custom branding for boot, installation screen, and login screen, and VPN and dev tools installed and configured by default, at a fortune 500 tech company.