In the early days of hobby humanoid robotics even simple tasks, like walking up a couple of stair steps, was a major challenge. The first robots lacked gyros for balance and used servos that weren't specifically designed for robot use. Later, as gyros became more commonplace, the top robot builders were able to accomplish climbing stairs, with varying results, but the servo power left something to be desired.
Now, with the benefit of high power servos and better, easier to use and program, some off-the-shelf humanoid kit robots, like the Kondo KHR-3HV, can conquer the task fairly easily, as Shibata-san with LIGHTFOOT Robotics demonstrated below.
Shibata-san put this particular demonstration together for an upcoming Robot Yuenchi event: