The ExtensionDescriptor class has been rehomed to neutron-lib and is being removed from neutron core, see [1]. All subproject maintainers should update their code to use the ExtensionDescriptor class from neutron-lib. I have submitted patches [2] for most subprojects. This will be highlighted in the next Neutron team meeting [3]. [1] https://review.openstack.org/398113 [2] https://review.openstack.org/#/q/status:open+topic:ExtensionDescriptor [3] https://wiki.openstack.org/wiki/Network/Meetings