  Interpretation of extensive air showers (EAS) experiments results is strongly
based on air shower simulations. The latter being based on hadronic interaction
models, any new model can help for the understanding of the nature of cosmic
rays. The EPOS model reproducing all major results of existing accelerator data
(including detailed data of RHIC experiments) has been introduced in air shower
simulation programs CORSIKA and CONEX few years ago. The new EPOS 1.99 has
recently been updated taking into account the problem seen in EAS development
using EPOS 1.61. We will show in details the relationship between some EPOS
hadronic properties and EAS development, as well as the consequences on the
model and finally on cosmic ray analysis.
