NixOS is mostly a rolling-release distro, like Arch, but it rolls a bit more slowly. You can opt into full rolling release with the "unstable" branch, which is very common. There's not a lot of benefit to "stable" IMO.
Er, no it isn't? Yes, unstable is rolling, but otherwise it has releases, like 25.11, which contain breaking changes. It cuts new releases quite quickly and drops old ones fast, but that doesn't make it a rolling distro.