Brand new, unopened. I got the wrong part in a larger shipment, and when I got around to installing it, I realized it was the wrong part (the cable is green and it's supposed to be yellow), but it was too late (by two days) to return it, so I want to sell it. If you are getting a P0138 code (or any other P013x or similar cat-related codes), it may be time to replace it (mine is in great shape).
This is a link to the part on the Subaru parts website so you can check compatibility with your car: https://parts.subaru.com/p/Subaru_2010_WRX/Sensor-Oxygen/49232650/22690AA900.html
It fits various models with turbo engines, between 2008 and 2014.
If the ad is still up, I still have it. The price is listed above: $160.