Starting from CubicWeb version 4.0 all code related to generating html views has been moved to the Cube cubicweb_web.
If you want to migrate a project from 3.38 to 4.* while still using all the
html views you need to both install the cubicweb_web cube AND add it to
your dependencies and run
cubicweb_web can be installed from pypi this way:
pip install cubicweb_web
In the long run cubicweb_api will be merged inside of CubicWeb.