  Extensive air shower detectors of gamma rays in the sub-PeV energy region
provide a new and relatively unexplored window for dark matter searches. Here
we derive some implications of the recently published Tibet AS$_\gamma$ data
for decaying dark matter candidates. The available spectral information is
already useful in obtaining competitive constraints, surpassing existing limits
above 10 PeV mass for hadronic or massive boson final states. This is
particularly true if accounting for a benchmark astrophysical background of
Galactic cosmic rays in the (0.1-1) PeV range. By relying on the arrival
distribution of the photons, we show that significantly better sensitivity can
be attained, comparable or better than IceCube also for most leptonic final
states. Full data exploitation requires however further information disclosure.
