  Since 2006, EPOS hadronic interaction model is being used for very high
energy cosmic ray analysis. Designed for minimum bias particle physics and used
for having a precise description of SPS and RHIC heavy ion collisions, EPOS
brought more detailed description of hadronic interactions in air shower
development. Thanks to this model it was possible to understand why there were
less muons in air shower simulations than observed in real data. With the start
of the LHC era, a better description of hard processes and collective effects
is needed to deeply understand the incoming data. We will describe the basic
physics in EPOS and the new developments and constraints which are taken into
account in EPOS 2.
