  The event generator Sibyll can be used for the simulation of hadronic
multiparticle production up to the highest cosmic ray energies. It is optimized
for providing an economic description of those aspects of the expected hadronic
final states that are needed for the calculation of air showers and atmospheric
lepton fluxes. New measurements from fixed target and collider experiments, in
particular those at LHC, allow us to test the predictive power of the model
version 2.1, which was released more than 10 years ago, and also to identify
shortcomings. Based on a detailed comparison of the model predictions with the
new data we revisit model assumptions and approximations to obtain an improved
version of the interaction model. In addition a phenomenological model for the
production of charm particles is implemented as needed for the calculation of
prompt lepton fluxes in the energy range of the astrophysical neutrinos
recently discovered by IceCube. After giving an overview of the new ideas
implemented in Sibyll and discussing how they lead to an improved description
of accelerator data, predictions for air showers and atmospheric lepton fluxes
are presented.
