I dont think they released OST yet. Im also waiting for it. This soundtrack is damn amazing. https://www.youtube.com/watch?v=uz_-B0Oxr1o
I believe it's a slowed piano cover of "Alive", the song that plays at the end of every episode. https://www.youtube.com/watch?v=V1QGd843bdo

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Does anyone have an info if it got released? Probably not since i cant find it anywhere, but who knows.