"Shimano has formally announced plans to release Dura-Ace Di2, a new electronic shifting option for the all-new 7900 series Dura-Ace, in January.
Comprised of dual control shift/brake levers, front derailleur, rear derailleur, a wiring harness and battery pack, the new Dura-Ace Di2 7970 components integrate with components from the upcoming 7900 series Dura-Ace group, while adding a total of only 68 grams.
Electrically-actuated shifting eliminates cable friction and contamination. The shifters are now merely switches, which also allows for creative placement of optional remote shifters while also reducing the weight and profile of the main shifting units. For example, a rider could place remote switches out on the ends of aero bars as well as on the top of drop bars near the stem.
Derailleur movements are computer-controlled and servo motors in both front and rear derailleur create synchronized shifts."