Currently the Python package specifies cffi<2, however, cffi only has wheels for Python 3.14 starting with v2. As a result, cffi must always be build from source when installing tableauhyperapi on a system with Python 3.14.
This is currently already affecting downstream projects trying to install the package in CI, which does not have the build requirements for cffi: innobi/pantab#419 (comment)