An optical network unit (ONU) of a gigabit-capable passive optical network (GPON) adapts to an optical line termination (OLT) to which it is coupled. The ONU determines a type of the OLT to which it is coupled, and based on the type, configures an optical transmitter of the ONU to be compatible with the OLT. The ONU can also determine which OMCI software stack to load based on the type of the OLT.