The Cosworth WRX STI CS400 is a limited (75 units) version of the Impreza WRX STI for the UK market. It includes a Cosworth-tuned version of the standard STI engine rated at , an upper mesh grille with piano black finish on the top frame, modified front bumper with "Cosworth" emblem on the lower mesh grille, 18-inch alloy wheels, lip front spoiler, rear waist spoiler, Bilstein struts, Eibach springs, AP Racing's larger diameter ventilated front brakes with six-piston calipers, Recaro leather seats with "Cosworth" label, piano black center console panel, "Cosworth"-badged floor mats.
