According to the seller, Honda had an idea that it had something special with the CB750 and built four preproduction models to be shown off to American media in 1968. Each one was hand-built by Honda technicians from bespoke components, and this blue/green model was photographed by magazines and for promotional material at the time. The seller believes that one of the four prototypes was destroyed, one is in Europe and one is unknown, which means this may be the only chance for collectors to get their hands on one.
The bike has prompted quite a bidding war with 97 bids registered as of this writing. With about seven hours left to go in the auction, the top big currently sits at $135,300. At this rate, things could get very exciting at the end. Although to own a prototype for the first super bike, it might be worth it.