South Korean quadruped robot finishes 42-kilometer marathon in 4 hours 19 minutes on single charge

Researchers from the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon have published findings detailing the performance of their four-legged robot, Raibo2. The quadruped completed an official 42-kilometer marathon in Sangju, South Korea, in approximately 4 hours and 19 minutes on a single battery charge. Although the road race occurred nearly two years prior, the peer-reviewed results appeared in the journal Nature on 23 September 2026. To safeguard nearby participants along the open course, scientists guided the machine directly rather than relying entirely on its autonomous navigation. A team of 20 researchers alternated in an escort relay to monitor the robot throughout the event following a month of specialized training.

First author Jemin Hwangbo noted the reaction from fellow competitors along the route.

Other runners cheered him on. Some people who could run faster even started running next to him.

Engineering and movement efficiency

The endurance of Raibo2 does not stem from a larger battery pack, but from lightweight physical components and optimized control systems. Engineers developed lighter robotic legs and enhanced the drive circuitry to minimize thermal and electrical losses during continuous operation. Gait cycles were trained using machine learning algorithms to reproduce the fluid, energy-saving strides seen in human long-distance runners. These mechanical and algorithmic refinements allow the system to operate three times longer on a single charge than competing quadruped models. Upon crossing the finish line after 42 kilometers, the machine retained sufficient battery reserves to travel an estimated 25 additional kilometers.

Hwangbo explained the biomechanical approach behind the machine's running style.

Just like professional human marathon runners, this model makes optimal movements for minimal energy waste.

Overcoming energy barriers in legged robotics

Legged machines offer distinct navigational advantages over wheeled platforms when traversing stairs, mountain paths, and uneven disaster rubble. However, four-legged configurations traditionally suffer from high power consumption because every step requires the mechanical actuators to absorb and stabilize the robot's entire mass. Traditional approaches frequently added structural reinforcement to enhance physical resilience, which increased overall weight and further depleted onboard energy stores. Excess weight also degrades dynamic stability, creating severe balance issues in bipedal systems and limiting the operational range of four-legged units.

Search, patrol, and commercial potential

The extended operating range broadens the scope of tasks that quadruped platforms can perform in remote environments. KAIST researchers expect the platform to assist in delivery routes, security patrols, and emergency response operations across mountainous terrain where battery swapping remains impractical. Independent robotics specialists emphasize that reducing component weight also lowers manufacturing expenses across the wider robotics sector. Lower production costs could facilitate the development of affordable assistive humanoids for eldercare and domestic assistance.

Maarten Steinbuch, a robotics professor at Eindhoven University of Technology, described the manufacturing benefits of lightweight construction.

We strive for robustness, but that makes the whole thing very heavy. Because this new design simply uses less and lighter material, costs also go down.