This is the original Subaru STi compressor bypass valve. (The compressor bypass valve, also known as a "blow off valve," releases compressed charge air when you back off the throttle.).
Yes, the valve DOES come with the cast elbow part, as shown. No, you cannot buy that cast elbow part separately. The CBV gasket, on the other hand, is not included, and is sold separately HERE.
Fits all 2002-2007 WRX, and 2004+ STI, including 2015+ STI.