Synapse (the Matrix server implementation) is moving to an AGPL+CLA model.
Their announcement reminds us that this allows them to ship non-open-source derives in exchange for a fee. The wording is very clear: they intend to move from an open source model to an open core model.
Take great care when relying on this software. All the legal elements are in place so as to pull the rug from under you and screw over the community. There is no ambiguity here.
@blake @whynothugo from what I've seen they forked Synapse away from the Matrix foundation's version to do that, this has nothing to do with the protocol itself.