Flexible and adaptive tracked robots show the capacity to navigate in unstructured terrain, with a passive adaption of the track or a morphology change for terrain adaptation. Extending the concept to one in which the morphology can be actively changed has the potential to increase the capabilities of a locomoting robot while reducing the need for complex controllers and onboard navigation systems. This article introduces FLEXIV, a 232-g untethered robotic vehicle with flexible, magnet-equipped tracks that achieves adaptive locomotion across diverse geometries of ferrous terrains with appropriate transitioning of its track shape from circular to oblong. By modulating the configuration of a track loop, the robot can adjust its driving capability, such as traction and steering ability, to optimize its behavior to the terrain. This deformable robot is combined with an autonomous controller that leverages only robot posture information through inertial measurement units (IMUs) for terrain estimation to autonomously adapt the robot’s configuration to the environment. This enables the robot to autonomously navigate complex terrains, including diverse slopes and steps, and offers recovery actions for extreme falls.