In a more traditional SCT AD like Tapenade, there isn't really anything that corresponds to recording of program operations at runtime. Zygote arguably does som

In a more traditional SCT AD like Tapenade, there isn't really anything that corresponds to recording of program operations at runtime. Zygote arguably does something semantically equivalent to recording a trace (at the interprocedural level), but of course the idea is that once you've optimised that away we approximate Tapenade – so the line is a bit blurred. Don't get me wrong, I agree with your core point: "tape-free" conflates multiple things, and none of them really capture the AD design space in a useful way. Hopefully as the field settles down we'll figure out more useful axes for comparing these tools.