1. A method for operating a hybrid drive system comprising: ascertaining an overall cost function that takes into account a cost function which is a function of an operating point for minimizing an energy usage of the hybrid drive system, and that takes into account one or more partial cost functions which are a function of the operating point, which are each assigned to a requested special function; determining an optimized operating point of the hybrid drive system corresponding to an optimization of overall costs according to the ascertained overall cost function; operating the hybrid drive system at the operating point; and executing those of the requested special functions for which the determined operating point is within an operating range assigned to the respective special function.