As Jitender Nandal told, the Expi cell lines (both CHO and 293) are cells respectivelly derived from the CHO-S and HEK293.
Since those cells are proprietary of Thermo, there are not many information about the modifications. It seems that the cells were not subjected to any genetic modification but just adapted to growth in suspension in the rich and BSA free EXpi expression mediums which allow to them to growth until very high cell densities and therefore reach high specific protein expression yields.
In my experience both EXpi cell lines are certainly expensives but very powerful.
In my experience, the Expi293 work very well for the production of recombinant proteins or fab antibodies while the EXpi-cho guarantee higher yields for expression of full lenght mabs.
You can find some more information about if on my blog (PROTEOCOOL):