  The Monte Carlo model Sibyll has been designed for efficient simulation of
hadronic multiparticle production up to the highest energies as needed for
interpreting cosmic ray measurements. For more than 15 years, version 2.1 of
Sibyll has been one of the standard models for air shower simulation. Motivated
by data of LHC and fixed-target experiments and a better understanding of the
phenomenology of hadronic interactions, we have developed an improved version
of this model, version 2.3, which has been released in 2016. In this
contribution we present a revised version of this model, called Sibyll 2.3c,
that is further improved by adjusting particle production spectra to match the
expectation of Feynman scaling in the fragmentation region. After a brief
introduction to the changes implemented in Sibyll 2.3 and 2.3c with respect to
Sibyll 2.1, the current predictions of the model for the depth of shower
maximum, the number of muons at ground, and the energy spectrum of muons in
extensive air showers are presented.
