Physical AI’s Biggest Challenge Is the Last 50 Feet

Last-mile delivery, the final leg that moves a package from a local hub to a customer’s door, already accounts for more than half of total supply chain costs, and U.S. carriers spend an estimated $90 billion a year on that leg alone, according to industry estimates cited by Boston Dynamics. Almost all of that expense comes from human drivers walking packages down driveways and up stairs for hours at a stretch. The unsolved problem is not the road, but the last 50 feet between the curb and the customer’s doorstep.

“So much of logistics is already automated, but we believe that the final frontier of logistics automation is that last 50 feet,” Marco da Silva, vice president and general manager for Spot at Boston Dynamics, said. Boston Dynamics is testing Spot, its four-legged robot, as a delivery assistant that rides in a van and carries packages to doorsteps. A driver loads boxes onto a conveyor payload on Spot’s back. The robot navigates curbs, stairs, gravel and ice before setting each package down. Boston Dynamics delivered a carton of eggs using Spot to demonstrate the system’s precision. The company has set a goal for its pilot program: Spot working alongside a driver to deliver 200 packages a day, five days a week. Spot costs roughly $75,000, according to The Next Web.

Largest Delivery Robot Fleet in the US Stops at the Curb

Serve Robotics shows what scale looks like when the terrain is flat. The company deployed more than 2,000 autonomous sidewalk delivery robots by the end of 2025, creating the largest sidewalk delivery fleet in the U.S., Serve Robotics announced. The fleet grew twentyfold in a single year through partnerships with Uber Eats and DoorDash across Los Angeles, Atlanta, Dallas-Fort Worth, Miami, Chicago and Alexandria, Virginia. Serve’s robots operate at Level 4 autonomy, meaning they run without a human safety driver, and complete 99.8% of deliveries. They cannot climb stairs.

DoorDash’s Dot robot, deployed in Arizona since late 2025, fits through doorframes but also cannot climb stairs, The Next Web reported. Serve and DoorDash have proven that sidewalk delivery works at commercial scale. Nobody has done the same for the doorstep.

Both Amazon and Boston Dynamics Want to Solve the Last 50 Feet

Amazon acquired Rivr, a Zurich-based robotics startup, in March 2026 and plans to test its four-legged wheeled robots as a way to help delivery associates carry packages to customer doorsteps, CNBC reported. Unlike Amazon’s earlier Scout sidewalk robot, which the company shut down in 2022, Rivr’s machines can climb stairs and cross uneven terrain, TechCrunch reported. Rivr had raised $25 million in total funding and was last valued at about $100 million, TechCrunch reported. Amazon had previously invested in Rivr through its $1 billion Industrial Innovation Fund, CNBC reported.

Spot uses four legs to walk, giving it agility on highly unstructured terrain. Rivr uses a hybrid of wheels and legs, prioritizing speed on flat surfaces while retaining the ability to climb stairs. “Companies have tried drones for delivery, but they haven’t been able to get to the porch, and so packages were being left in the middle of the yard,” Paige Miller, Spot’s product manager at Boston Dynamics, said. “We’ve also seen the struggles of various wheeled robots for last-mile delivery.” Neither company has answered, at scale, whether the hardware’s cost can be justified by the number of deliveries it handles per day.

Nvidia CEO Jensen Huang said at CES in January 2026 that the ChatGPT moment for robotics had arrived, PYMNTS reported. The thesis that follows is whoever deploys the most robots collects the most operational data, and that data trains the next generation of models. Serve’s sidewalk fleet is already gathering that data on flat terrain, while Boston Dynamics and Amazon are betting on the porch. The robot that can reliably climb a set of stairs, leave a package at the right door and do it at a volume that justifies the hardware cost has not yet been built.