> My understanding is that coarrays are a modern replacement for MPI Well, yes and no. Co-arrays are a higher level abstraction, belonging to the category of P

> My understanding is that coarrays are a modern replacement for MPI Well, yes and no. Co-arrays are a higher level abstraction, belonging to the category of Partitioned Global Address Space (PGAS). Depending on the implementation, co-arrays might very well be implemented on top of a MPI library (as there has been a huge amount of work making MPI fast over all kinds of fancy interconnect fabrics).