Ah, ok, that makes more sense then. The "implemented in. Not a clone" made it sound like the actual, core language implementation had been switched over to Go... and clearly that didn't sound right.
Right, the reference Tcl implementation is still in C. This project takes the C code and produces Go, along with a supporting libc emulation in Go. It's still the original C code, not a clone as Jim or Picol.
Thanks for the clarification. I don't use Tcl for normal work anymore (though I still use it for small things), but it still has a very special place in my heart. It's one of my favorite languages to program in.