Pictures taken at Silverstone this weekend have uncovered that Red Bull have adopted or are at least testing an exhaust chamber. Also known as a Helmholz exhaust, the regular exhaust pipe features a blind additional branch which can accumulate exhaust gases when pressure is high in the exhaust pipe. It can then release those gases again when the driver gets off the throttle, hence evening out the pressure differences that occur in the exhaust pipe.
Apart from the evening out in an attempt to gain a more constant exhaust flow - and hence a more constant rear downforce at the diffuser - a Helmholz resonance chamber can also help the "Kadenacy Effect" in a specific RPM range of the engine.
The Kadenacy effect is an effect that forms from pressure-waves in gases. In essence, careful design of the dimensions and position of the exhaust changer can assist scavenging of exhaust gases out of the cylinders and therefore increase the pressure drop across the intake and exhaust valve area within a specific RPM range. As such it could be used to increase engine performance in the engines' most used RPM range.
To make room for the exhaust chamber that Ferrari debuted in F1 through 2011, RBR redesigned the entire exhaust of the RB8. While it previously ran close to the car's engine heat cover and then curved downward with a 180° turn, the final turn is now curved upwards, similar to Williams' exhaust layout.
Also note, as marked with yellow, the upward direction of the final 10cm of the exhaust pipe. The regulations specify that this must be a straight, circular section pointing up between 10° and 30°.