It is a limited (900 units) version of the Impreza WRX STI for the Japanese market. It included engine, suspension, and body parts improvement over the regular model. The ball bearing on the turbine axle was modified to reduce friction, the ECU retuned for better response, and an intercooler water spray fitted. The cross member, suspension and power steering were also improved for better handling and body rigidity. An aluminum hood, laminar window glass, and a lighter battery helped to reduce weight.

Debuting at the Tokyo Auto Show in October 2007, WRX STI versions build further on the standard WRX cars. The STI available in Japan is fitted with the 2.0-liter EJ207 engine with twin scroll turbocharger generating 227 kW (308 PS) at 6,500 rpm and 422 N⋅m (311 lb⋅ft) of torque at 4,400 rpm. Export markets receive the higher-displacement 2.5-liter EJ257 unit with the single-scroll VF48 turbocharger rated at 221 kW (300 PS) and 407 N⋅m (300 lb⋅ft) of torque. The turbocharger directs air through a larger top-mount intercooler which has lost the red "STI" that was on previous generations. The STI (3,395 lbs) is heavier than the WRX (3,174- 3,240 lbs depending on trim) due to a more robust transmission, rear differential and other chassis reinforcements.

Subaru Impreza WRX STI GV sedan (facelift)
Like the standard WRX, the third generation model was shortened to "Subaru WRX STI", with the Japanese markets notably abstaining from this convention. To differentiate the STI from the regular WRX, Subaru opted to manufacture the STI with a wider body and therefore track—as noted by the flared wheel arches. Furthermore, Subaru utilized aluminum suspension components for the STI. Electronic modifications include a multi-mode electronic stability control with "normal", "traction", and "off" modes; Subaru Intelligent-Drive (SI-Drive) with three modes: "intelligent", "sport", and "sport sharp"; and multi-mode driver controlled center differential (DCCD). The DCCD is a combined mechanical and solenoid operated limited-slip differential which enables the driver to switch between manual and automated centre differential locking. The locking strength can vary from fully open to fully locked [27] with a 40/60 front/rear open torque bias.

The STI hatchback was released in the United States in March 2008.

A Subaru Impreza WRX STI Group R4 was entered in the 2012 FIA Asia-Pacific Rally.

In 2010 for the 2011 model year, the WRX STI became available as a four-door. The most noticeable feature on the STI sedan is a large rear spoiler. Australia also received the 2011 model year STI as a sedan to complement the hatchback released in 2008. Australian STIs were offered in standard form, plus the STI spec.R. An electric sunroof, leather upholstery, satellite navigation, and BBS wheels are standard on the spec.R, while Recaro seats are optional.

A facelift of the STI arrived in 2010 for the 2011 model year, distinguished by a new front bumper. Tweaks to the suspension—stiffer springs, larger anti-roll bars, new pillow ball bushings on the front lower arms, as well as wider standard tires—had the effect of improved handling.[29]

As of March 2022 Subaru have confirmed "there will be no STI variant for the new generation Subaru WRX" – leaving the standard WRX and its 202 kW/350Nm engine as the most powerful version of the rally legend the company will build

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