pybind11 runtime dependency for CPPE?

[boegel]

In an environment where CPPE is installed, "pip check" fails unless pybind11 is also installed:

$ pip check
cppe 0.3.1 requires pybind11, which is not installed.

$ echo $?
1

Is pybind11 really a runtime dependency of CPPE, or is it only required when building/installing CPPE?