Abstract : AC losses are one of the key parameters in sizing High Temperature Superconducting (HTS) large scale devices. Therefore, their estimation has to be realistic in order to properly design the cryogenic system. Thus far, various 3D numerical models have been developed to that goal. However, the lack of analytical solutions in most of the cases and the scarcity of the experimental data leave the accuracy of the numerical methods an open question. In this paper, a benchmark on the 3D numerical modeling of a superconducting bulk is introduced. After a detailed description of the methods and their implementations, the results obtained by various independent teams are compared and discussed. This paper can be defined as a beginning of a conjoint work on 3D modeling of HTS bulks.