Search for dark matter using sub-PeV <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>?</mml:mi></mml:math> -rays observed by Tibet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow><mml:mi>AS</mml:mi></mml:mrow><mml:mi>?</mml:mi></mml:msub></mml:math>

The discovery of diffuse sub-PeV gamma-rays by the Tibet AS$_\gamma$ Collaboration promises to revolutionize our understanding high-energy astrophysical universe. It has been shown that these data broadly agree with prior theoretical expectations. We study impact this on a well-motivated new physics scenario: PeV-scale decaying dark matter (DM). Considering wide range final states in DM decay, number density profiles, and numerous background models, we find provide most stringent limit lifetime for various Standard Model states. In particular, strongest constraints are derived masses between few PeV tens PeV. Near-future can be used discover DM.