Based on an examination of the migration notes, it appears that there is at least one change which would break gaek, specifically the removal of google.appengine.api.namespace_manager which has no replacement.
The migration notes state:
There is no replacement for google.appengine.api.namespace_manager which is used to determine the default namespace when not passed in to Key()
This seems to primarily affect envrion.py which imports namespace_manager and makes its methods available.
As noted in #20 :
The migration notes state:
This seems to primarily affect
envrion.pywhich importsnamespace_managerand makes its methods available.