It's the Switchback tank. And it's on sale now...
I've had it for years. I saw a couple of others that looked great recently, but the reviews were horrible; the things are too tight. I bought another style of Athleta top around the same time as the Switchback and I ripped it the first time I wore it, because I couldn't get it off! I don't mind the tightness when they are on, but please, I shouldn't have to be a contortionist to get a top off.