@Carla_Becker, we have just changed how some of the data is built but have not updated the docs yet. Sorry for the confusion. You can instead ask for bulk_modulus or bulk_modulus.voigt to get what you need in fields.
@jessechen the latest API client has support for querying elasticity data using a list of MPIDs. If you update to v0.38.0 it should work now.
– Jason