A white Subaru BRZ with STI badges has been spotted lapping the Nürburgring. While STI badges on the WRX have always represented higher performance, the additional aerodynamic body modifications of this BRZ seem to confirm what we’ve expected is coming: a Subaru BRZ STI. For more on how the Subaru BRZ STI fits into Subaru’s future performance lineup with the upcoming WRX, read our update from Peter Lyon below.

A carbon fiber air splitter sits at the bottom of the front fascia, while larger brakes with black-painted calipers peek out from behind what appear to be 18-inch alloy wheels featuring a similar design to the BBS wheels found on WRX STI models. STI badges can be found on the brake calipers and wheel center caps. Around back, a large wing (likely made of aluminum and carbon fiber) is placed on the deck lid.

Though it’s unclear what’s under the hood of this Subaru BRZ STI, the lack of a hood scoop – a turbocharged Subaru hallmark – suggest this non-turbocharged model is designed with handling and braking improvements in mind. But considering that several aftermarket tuners have fit turbochargers and superchargers into BRZ and FR-S engine bays, don’t be surprised to see a more powerful BRZ or FR-S variant in the future.

At a recent SEMA show preview, six out of seven Scion FR-S models were fitted with superchargers. As for turbochargers, Accelerated Performance has a turbocharger setup for the BRZ and FR-S that is claimed to be capable of more than 400 hp. Whatever the future holds for the BRZ, we’re looking forward to a potential production model based on the prototype seen in the gallery below.

We’ve heard more on the future of the Subaru BRZ from our foreign correspondent Peter Lyon. Here’s what he’s learned about upcoming BRZ variants:

Though the BRZ STI concept unveiled at the Tokyo Auto Salon last January lacked a hood scoop that signifies a turbo, all the indicators pointed to Subaru giving its new coupe some real extra punch in the form of a turbo. Well now that the BRZ STI has been spied testing on the Nürburgring, I can categorically say that it does not have a turbo.

My source says the exhaust note sounded “beefier,” signaling that Subaru engineers may have tweaked the engine by fitting a high-performance exhaust system and perhaps even an uprated ECU delivering around 220-230 hp (up 20-30 hp). And that all makes sense because from what I am hearing, Subaru’s marketing staff wants to position this STI under the soon-to-be-launched all-new WRX — so we can’t have the BRZ producing more power than the next WRX.

Fitted with what looks like new lighter, larger, high performance wheels, my source tells me the BRZ STI also cornered flatter than the stock BRZ generating far less body roll. This would indicate that the car has been given some special STI springs and dampers, which would no doubt have been developed at the Nürburgring. It also employs significantly upgraded brakes in the form of the STI 4-piston variety, replacing the stock car’s floating setup.

One source close to Subaru in Japan tells me that we can expect to see the BRZ STI land in showrooms as early as spring 2013 (in Japan) and soon after that in the U.S.