It's not listed and hasn't been measured, but from my very scientific experiments, it's very low. Using it with my IEMs that are hissy AF on my Pixel: Andromeda Gold is the hissiest by far. Quite noticeable on tracks that have a black background or when no music is playing. Shure 846, surprisingly, very little hiss despite it's stupid low impedance. Never noticeable while music is playing. Solaris is somewhat hissy. Not as bad as the Andro, but worse than the 846.
I normally use an IEmatch with my Pixel for all 3 of these, but would only use it with the Andro Gold in this scenario.
So while I can't confirm its exact OI, it's low enough to never have an issue except for the hissiest of IEMs. This was all done for SE, didn't try XLR.