The 1872 Cup, contested by Edinburgh and Glasgow Warriors, will follow a “best of three” format this season, Scottish Rugby have confirmed.
A third derby, taking place on the final weekend of the Pro14 season, has been added to the expanded league.
Previously, the cup had been awarded to the aggregate winner of the two existing inter-city Pro12 matches.
Edinburgh host rivals Warriors on 23 December, before travelling to Scotstoun seven days later.
The final meeting of the sides takes place at Murrayfield on the weekend of 28 April.