This page is expected to capture all the relevant information about potential and real neutron library API breakages that go merged in the tree.
Neutron started to spin out both advanced services (LBaaS, VPNaaS, FWaaS) and vendor plugins and ml2 drivers into separate git repositories in Kilo. Code that was already split out still uses lots of symbols from neutron.* namespace, assuming neutron is a library with stable API. It's not really the case, and so there may be changes in the tree that will break external code (*aas, vendor libraries) that use those symbols.
The idea is to eventually stabilize some parts of neutron tree and convert them into a public library with some kind of API stability guarantees. That said, it's not going to happen immediately, so breakages are expected in the short term.