Aha, checking the version of tcl is explained in the aolserver installation guide.
https://openacs.org/doc/current/aolserver4.html
or simply:
[root root]$ tclsh
[root root]% info exists tcl_platform(threaded)
1
#This is to check that it is threaded.
[root root]% info patchlevel
8.4.7
[root root]%