The number of active antenna ports used for uplink and/or downlink MIMO transmissions to a given user are dynamically adjusted, based on user data traffic payload size per period of time, and based on RF conditions. An example method, in a radio transceiver that supports two or more MIMO transmission and reception modes, begins with evaluating channel conditions between the radio transceiver and a remote wireless device and comparing a throughput demand for the remote wireless device to a forward link capacity and/or reverse link capacity. A forward link transmission mode or a reverse link transmission mode is changed, based on the channel conditions and the throughput demand. The transmission mode is changed from a first multi-stream mode to a second multi-stream mode having fewer streams than the first multi-stream mode, despite that channel conditions for the corresponding link support the first multi-stream mode.