MCPL_input reads the events of an MCPL file as the starting rays of a simulation and sets the number of rays to the number of events in the file times repeat_count. As in KDSource, the resulting stream of rays is split into one contiguous chunk per MPI process. With repeat_count\(>1\) the events are replayed, with the weights divided accordingly; every replay after the first is smeared in velocity, position and/or direction (v_smear, pos_smear, dir_smear), so at least one of these must be set. By default the file is shared between the MPI processes, so –mpi=N does not change the number of rays. Setting replicate_across_processes=1 restores the behaviour from before Oct 2026: repeat_count is rounded up to a multiple of the number of MPI processes, so that each process runs through the whole file. The former MCPL_input_once is now an MCPL_input with repeat_count=1 forced, in the obsolete category.