1. A computer server system comprising: one or more hardware processors; and a non-transitory computer storage medium encoding instructions that when executed by the one or more hardware processors cause the computer server system to perform operations comprising: receiving a single message requesting to sync data associated with multiple dataclasses with at least one client device, wherein the message includes a proposed sync mode for each of the multiple dataclasses, negotiating the proposed sync mode for each of the multiple dataclasses in parallel responsive to receiving the message, and sending a reply message that includes one or more status codes indicative of whether the proposed sync mode for each dataclass has been accepted by the computer server system.