1. A method for operating a drivetrain of a motor vehicle, comprising the steps of: ascertaining at least one variable, which quantifies and/or influences a movement of the motor vehicle, by determining respective single-wheel speeds, a steering wheel motion, a steering wheel angle gradient, an accelerator pedal value, an accelerator pedal value gradient, a brake pedal value, a transversal acceleration of the motor vehicle, a yaw rate of the motor vehicle, a longitudinal acceleration of the motor vehicle and/or an actual gear ratio of the motor vehicle are determined; activating an all-wheel drive of the motor vehicle as a function of the variable; based on the at least one variable, assessing whether a relevant driving situation is imminent; and, only if affirmative, activating the all-wheel drive activated before onset of the relevant situation, wherein said relevant driving situation involves a driving situation in which a deviation between an actual responsiveness of the motor vehicle and a responsiveness dictated by a driver can be expected, or a driving situation in which the driver is able to resolve different handling characteristics between single-axle operation and all-wheel operation; and once the all-wheel drive has been activated, determining on the basis of the at least one variable and/or further variables, which quantify and/or influence the movement of the motor vehicle, whether a deactivation of the all-wheel drive would lead to said relevant driving situation, and if this is not the case, deactivating the all-wheel drive after a defined holding time.