Porsche is planning to facelift the 911 lineup in 2015 when they will also introduce the GTS version seen here with probably a naturally-aspirated flat-six 3.8-liter engine derived from the Carrera S but uprated to deliver as much as 425 PS (312 kW). Power could be sent to an all-wheel drive system through a manual transmission although this hasn't been confirmed.
In terms of design, it's hard to spot any differences between these prototypes and the available 911s but we do notice a different rear end with central exhausts. The body should be a tad wider and will feature bespoke engine cover venting along with vents behind the rear wheels. Just like the previous iteration of the GTS, the 991 generation should come with center-lock wheels.
An official reveal could occur before the end of the year, with sales commencing in 2015.