Can I run E85 or an ethanol blend in a 2022+ WRX?

Not as the car sits. The VB is not a flex fuel vehicle from the factory - the ECU has no way to know what is in the tank, and the stock tune assumes pump gasoline. Putting E85 in an unmodified VB means the engine runs dramatically lean for the fuel, which is the condition that damages engines rather than the one that makes power. Done properly, though, ethanol is the single best value modification on this platform. What properly means: a flex fuel sensor kit, roughly $440, which reads actual ethanol content and reports it to the ECU. A tune written for flex fuel, roughly $575. And for anything beyond mild power, an upgraded low pressure fuel pump - ethanol needs roughly 30 percent more fuel volume than gasoline and the factory pump runs out. A 340 lph pump is around $190. Why bother: on a documented FA24 dyno ladder, a Stage 1 car on 93 octane measured 260.6 whp while the same Stage 1 car on E85 measured 289.4 whp. That is roughly 29 wheel horsepower from fuel alone, which beat a full Stage 2 hardware package on pump gas that measured 274.7 whp. Ethanol does more on this engine than the parts do. Why the sensor matters rather than a fixed E85 map: pump E85 is not consistently E85. Blends vary by station and by season, and winter blends can drop well below the label. A flex fuel sensor lets the ECU read actual content and adjust continuously. A fixed ethanol map on a tank that turned out to be E60 is how people find the knock limit expensively. On blends specifically - E30, E50 and similar mixes of pump gas and E85 - these are entirely viable and are how many owners run the car. With a flex fuel sensor and a proper tune the ECU handles whatever is in the tank, so you can fill with whatever is available and the car adapts. Without the sensor, blending is guesswork with real consequences. The costs to accept: fuel economy drops 20 to 30 percent. Range drops with it, so if there is no E85 station on your normal routes this becomes a genuine daily annoyance rather than a minor one. Ethanol is also harder on some fuel system components over long periods, and a flex fuel setup is clearly visible to a dealer in a way a flashable map is not. The short version: yes, with the right hardware and tune, and it is worth doing. No, not by simply filling up at the E85 pump, and doing that on a stock VB is a genuinely bad idea rather than a merely suboptimal one.