I'm not convinced that issues requests from the multiple clients for the same key actually matters. My speculation is that they map a key to their backend via some type of (consistent/rendezvous) hash and then ensure that all requests for said key lands on the same process/server* that contains the state for the key.
This means that for a specific key, you end up on 1 specific process. If you can ensure this, you basically get monotonic reads/writes along with RYW and Writes-Follow-Reads. All this maps to causal consistency so it is believable.
* The request could probably be sent to a read-only replica first but it could then forward it to the leader replica handling writes by examining some logical timestamp.
This means that for a specific key, you end up on 1 specific process. If you can ensure this, you basically get monotonic reads/writes along with RYW and Writes-Follow-Reads. All this maps to causal consistency so it is believable.
* The request could probably be sent to a read-only replica first but it could then forward it to the leader replica handling writes by examining some logical timestamp.