The S209’s modifications are so significant, it has to be assembled at STI’s facility.
Subaru finally answered the prayers of its American enthusiasts with the debut of the WRX STI S209 at the 2019 Detroit Auto Show, which is the most powerful WRX STI Subaru has ever built for America. Expect it isn't really a Subaru. As Jalopnik explains, the S209 is technically an STI.
Unlike the regular WRX STI that has been sold in America since 2004 as a high-performance trim, the S209 is first assembled by Subaru before being shipped to STI's facility to be completed. Here, STI makes some significant modifications to the S209, adding wider fenders, new 19x9 STI BBS wheels, unique 265/35R19 Dunlop GT 600 performance tires, and its flexible front-strut tower bar and flexible front and rear draw stiffeners.
Under the hood, the S209 also gets a significantly revised version of Subaru's flat-four that produces 341 horsepower, up from 305 hp. The S209 even had to be homologated for sale in the US as an STI rather than as a Subaru.
You may be wondering why all this is necessary. Apparently, it's because regular Subaru cars have different production standards. For example, Subaru cars require a certain amount of space between a tire and bodywork. This could force STI to use a smaller tire size or a different alignment, but this isn't an issue if the car is developed in-house at a different factory.
"Subaru has their own ways, set up for mass production, but there are particular areas [of focus] people want for performance cars," North American business planner Yoshihide Yano revealed. "Having STI focused more on performance standards will let us try harder for performance."
At maximum capacity, STI is only capable of building five cars a day. With S209 production, they can pump out just two cars a day. For comparison, Subaru's Gunma assembly plant where the normal WRX STI is built is capable of building more than 900 cars a day.
Pricing for the Subaru WRX STI S209 hasn't been announced yet, but expect it to command a significant premium over the regular version, which starts at $36,095.