That manifest might be a nice way.

Another (also in the linked forum) is

readlink /nix/var/nix/profiles/per-user/root/channels-1-link 

And also, perhaps the easiest one:

cat /nix/var/nix/profiles/per-user/root/channels/*/svn-revision 

That manifest might be a nice way.

Another (also in the linked forum) is

readlink /nix/var/nix/profiles/per-user/root/channels-1-link 

And also, perhaps the easiest one:

cat /nix/var/nix/profiles/per-user/root/channels/*/svn-revision 

On newer versions of nix, the full git commit sha will also be in:

/nix/var/nix/profiles/per-user/root/channels/*/.git-revision