The filing does not state that these Data Center satellites will be any smaller than the Starlink v3.0 models. Initial units will likely be the same size as v3.0 so they can utilize the existing dispenser in the Starships. Electrical power needs will be high, so large solar arrays.
SpaceX will try to solve orbital data center challenges like latency, maintenance, or traffic with a new satellite constellation. It has filed for permission to launch up to a million of those.