I dug into iMessage a bit a while back, and it appeared that Apple held the keys for encrypted chats to allow messages to be sent to multiple devices that a per

I dug into iMessage a bit a while back, and it appeared that Apple held the keys for encrypted chats to allow messages to be sent to multiple devices that a person owns (laptop, iPad, iPhone), insulating the sender from having to know about each possible destination device. If the server has access to the keys, or can add their own key to a set of keys handed to clients during encryption, that fails to meet some definitions of 'end to end' encryption, since a server compromise will also compromise messages. Has the implementation changed in this regard?