Because the CHIPS event generator was originally developed only for final state hadronic fragmentation, the initial interaction of projectiles with targets requires further development. Hence, the first applications of CHIPS described interactions at rest, for which the interaction cross section is not important , , and low energy photonuclear reactions , for which the interaction cross section can be calculated easily . With modification of the first interaction algorithm the CHIPS event generator can be used for all kinds of hadronic interaction. The Geant4 String Model interface to the CHIPS generator ,  also makes it possible to use the CHIPS code for nuclear fragmentation at extremely high energies.
In the first published versions of the CHIPS event generator the class G4Quasmon was the head of the model and all initial interactions were hidden in its constructor. More complicated applications of the model such as anti-proton nuclear capture at rest and the Geant4 String Model interface to CHIPS led to the multi-quasmon version of the model. This required a change in the structure of the CHIPS event generator classes. In the case of at-rest anti-proton annihilation in a nucleus, for example, the first interaction occurs on the nuclear periphery. After this initial interaction, a fraction (defined by a special parameter of the model) of the secondary mesons independently penetrate the nucleus. Each of these mesons can create a separate quasmon in the interior of the nucleus. In this case the class G4Quasmon can no longer be the head of the model. A new head class, G4QEnvironment, was developed which can adopt a vector of projectile hadrons (G4QHadronVector) and create a vector of quasmons, G4QuasmonVector. All newly created quasmons then begin the energy dissipation process in parallel in the same nucleus. The G4QEnvironment instance can be used both for vacuum and for nuclear matter. If G4QEnvironment is created in vacuum, it is practically identical to the G4Quasmon class, because in this case only one instance of G4Quasmon is allowed. This leaves the model unchanged for hadronic interactions.
The convention adopted for the CHIPS model requires all its class names to use the prefix G4Q in order to distinguish them from other Geant4 classes, most of which use the G4 prefix. The intent is that the G4Q prefix will not be used by other Geant4 projects.