I, Robot (film)/WMG

Detective Spooner and Dr. Calvin were carried up the steps of the US Robotics building by Sonny.

This explains how they got to the top floor via the steps and were not out of breath. Sonny has strength - he managed to throw Alfred Lanning out the window and left dents in the table when frustrated about being interrogated. Carrying two adults up the steps probably isn't outside of his abilities - it just would have looked downright silly being shown onscreen.

Sonny and Spooner will team up as a detective duo

Sonny and Spooner, they fight crime. After all, he is capable of making decisions like a person and isn't bound by the three laws.