From Portal Puzzle Wiki
The Robot (also known as Beans and the Valuable Asset Retrieval Unit by fans) is a component of the Portal ARG.
The Robot first appeared on March 3rd, 2010, as part of a Portal update. The release notes for the update were simply "Added valuable asset retrieval." The Robot has apparently been dispatched by the BBS, as this update coincided with the BBS's addition of the line "-- VALUABLE ASSET RETRIEVAL INITIATED" and the progress bar.
While the Robot has not yet been shown, it is heard during the ending of the game: while Chell is lying outside (possibly unconscious) and debris of GLaDOS falls from the sky, it can be heard approaching. It then says "Thank you for assuming the party escort submission position," before dragging Chell away, presumably by the leg.
The Robot sounds mechanical (possibly hydraulic), and speaks with an accent. From the sounds of it approaching and leaving in Portal, it appears to be bipedal, weigh about 300 pounds, have a stride length of approximately half a meter. Additionally, due to its ability to drag Chell, it can be said that it has some form of grabbing implement. From the game's technical standpoint, The Robot uses a can of beans as a modus operandi, obviously not intended for canon (although d rattmann,s carrying of a can opener is).
Recently from GameInformer April issue, the robot that may had dragged Chell might resemble the Co-op bots, however, since Portal 2 takes place hundred of years into the future, it may have looked different.