The last time I covered the science of humanoid robots, the state of the art looked downright Orwellian — by which I mean, “four legs good, two legs bad.” It was 2015. Boston Dynamics’ first “Spot” quadruped had taken YouTube by storm, confidently trotting up stairs and recovering from vicious kicks. Also popular at the time: humanoids falling down. Constantly. I felt sorrier for those tottering metal lobsters than I ever did for Spot. Bipedal locomotion is hard.

Cut to now. Humanoids have apparently become so advanced that Tesla is mothballing some electric car models to make way for its Optimus humanoid robot, and start-ups are preselling android butlers with a straight face. Hype aside, I was genuinely curious: Did a paradigm shift happen in the field when I wasn’t looking? Sure, “AI” happened (that is, in the post-ChatGPT sense). I certainly hadn’t overlooked that. But I had no idea what it possibly had to do with robots not falling down anymore.

For a reality check, I called Scott Kuindersma, who recently left Boston Dynamics after many years there, and Jonathan Hurst of Agility Robotics. Both scientists had been present and involved during the robot-faceplant days. Surely today’s robotic bipedal marvels can ascend a few stairs and open a door without breaking a nonexistent sweat, something they famously struggled with a decade ago. I asked each researcher: Can your flagship robot — Boston Dynamics’ Atlas or Agility’s Digit, two of the most credible and pedigreed humanoids on Earth — handle any set of stairs or doorway?

“Not reliably,” Hurst said.

“I don’t think it’s totally solved,” Kuindersma said.

Don’t get me wrong: I don’t believe that some sock-faced robot zombie is close to taking over my household chores. But stairs and doors? It’s 2026. Why are humanoids still this … hard?