Thanks to a low pressure drop air cleaner and a performance muffler, the 2.0-litre turbocharged four-cylinder boxer engine now develops 221kW of power at 5600rpm, and 400Nm of torque between 2000 and 4800rpm.
Drive is sent to the ground via a standard all-wheel drive system, and a Lineartronic continuously-variable transmission (CVT) with an upgraded oil cooler and stronger radiator fan.
To improve the WRX's handling, the S4 tS is fitted with a Bilstein suspension setup, front tower brace, pillow ball bush rear suspension link, and 255/35 Dunlop Sport Maxx RT tyres mated to 19-inch BBS alloy wheels.
The S4 tS is marked out visually from other WRX S4 models thanks to its front splitter, and the red pin-striping on the grille surround and across the rear bumper.
On the inside, the tS features an upgraded instrument panel, STI-spec Recaro front bucket seats with silver highlights, plenty of STI and tS Limited Edition badging, and a leather gear shifter and steering wheel.
The WRX tS is available in both standard trim and with a more aggressively styled NBR Challenge Package, which features black alloy wheels, a suede-wrapped steering wheel, and a high-rise rear spoiler shared with last year's S207 limited edition model.
According to David Rowley, Subaru Australia's corporate affairs manager: “It’s a Japan domestic market project with no plans for that particular model in Australia. But, as always, we talk to the factory about what elements might be accessible to us at some stage in the future.”