Amazon's expanding fleet of robots includes: Hercules, a lifter capable of handling 1,250 pounds; Pegasus, which sorts packages on conveyor belts; and Proteus, the company's first fully autonomous robot able to operate directly alongside people.

Amazon is also looking to use a new generation of bipedal robots to help with the so-called "last-mile" of the delivery chain, where the process typically slows down, becoming far less direct and efficient.

Amazon hits 1 million robots and rolls out a new AI system to boost warehouse efficiency and automation. Here's what its robots do.