Image Credit: Porsche.Porsche has reached deep into its motorsport history for one of the wildest creations yet from its Sonderwunsch customization program. Called the Flachbau RS, this one-off machine transforms a 2018 Porsche 911 GT2 RS with the Weissach Package into a modern interpretation of the famous slantnose design.The project was commissioned by a Porsche enthusiast who wanted additional performance, Flachbau styling, and a rear wing inspired by the 911 GT3 R rennsport. Porsche teamed up with Manthey to develop the road-legal car, with specialists from Sonderwunsch, Style Porsche, Porsche Motorsport, and Weissach contributing to the three-year project.Its inspiration stretches back to the outrageous Porsche 935/78 race car, better known as "Moby Dick," whose aerodynamically optimized shape helped inspire the road-going Flachbau models of the 1980s. The German word "Flachbau" translates to "flat construction" and is closely associated with Porsche's distinctive slantnose 911s.AdvertisementAdvertisementAnyone hoping this signals the return of a regular-production slantnose 911 may be disappointed, however. Porsche confirms the Flachbau RS is a factory one-off, explaining the mysterious Flachbau and Flachbau RS trademark filings that appeared in 2025.The GT2 RS Gets A Completely Different FaceImage Credit: Porsche.The biggest visual change is naturally found up front, where the conventional 991-generation headlights and fenders have disappeared. Porsche created dramatically flatter front bodywork with extremely slim lighting, redesigned wheel arches, a new front bumper and splitter, while Manthey contributed additional aerodynamic elements.Those changes required considerably more engineering than simply fitting different body panels. Even the fuel-filler system had to be redesigned to accommodate the new front-end architecture, while the finished car still needed to meet the requirements necessary for road use.Grand Prix White paint provides another direct link to Porsche racing history, with contrasting graphics inspired by Moby Dick. The overall result mixes the unmistakable proportions of a 991-generation GT2 RS with a nose that looks unlike anything Porsche currently sells.Its 700-HP Flat-Six Was Already Powerful EnoughImage Credit: Porsche.The owner and Porsche agreed to keep the GT2 RS's 3.8-liter twin-turbocharged flat-six, which produces 700 horsepower and 553 lb-ft of torque, largely untouched.AdvertisementAdvertisementConsidering the standard GT2 RS was already one of the most ferocious road-going 911s ever produced, additional engine output was hardly necessary. Instead, Porsche concentrated its efforts on aerodynamics, weight reduction, and making the radically altered body function properly at extreme speeds.The Flachbau RS is nearly 70 pounds lighter than the already weight-conscious GT2 RS with Weissach Package. Porsche removed the infotainment and audio systems, reduced sound insulation and floor coverings, and even stripped unnecessary wires from the replacement wiring harness.Porsche Took The Aerodynamics SeriouslyImage Credit: Porsche.The giant rear wing is far from decorative. Its adjustable design offers multiple configurations, and in the High Downforce setting, Porsche says the Flachbau RS generates approximately 1,221 pounds of rear-axle downforce at its roughly 211-mph top track speed.Developing that package required the sort of testing normally associated with a production model rather than a privately commissioned one-off. Porsche built three test vehicles and conducted wind-tunnel and lighting evaluations, road testing, endurance work, and extensive vibration testing of the rear wing.AdvertisementAdvertisementTesting also included 50 laps of the Nürburgring Nordschleife, where Porsche evaluated the car's stability and aerodynamic behavior at speed. The rear wing's endurance program simulated loads equivalent to approximately 150,000 kilometers, or 93,200 miles, of customer use.The Interior Is Appropriately ExtremeInside, Porsche continued removing anything that did not serve the Flachbau RS's purpose. The infotainment screen has been replaced by a leather-trimmed storage compartment, while exposed painted metal and sections of the wiring harness emphasize the car's stripped-back character.Carbon-fiber bucket seats remain, along with special Flachbau RS embroidery and numerous bespoke details. A plaque identifying the car as a 2026 factory one-off leaves little doubt that this is something considerably rarer than even a normal GT2 RS.Porsche has not disclosed what the owner paid for the transformation, although the amount of bespoke engineering involved suggests this was an exceptionally expensive undertaking. For everyone else, the Flachbau RS offers a tantalizing look at what a modern factory-built slantnose can be, even if Porsche currently intends to build only one.AdvertisementAdvertisementWould you like to see Porsche put a modern Flachbau 911 into regular production? Does the slantnose design work on the 991-generation GT2 RS, or should Porsche have stayed closer to the cleaner shape of the 1980s originals?If you want more stories like this, follow Guessing Headlights on Yahoo so you don't miss what's coming next.