Version 2.0 of the Basic Model Interface (BMI) is a benchmark release, the result of a year of work in cleaning up, organizing, and standardizing language specifications and examples for C, C++, Fortran, and Python, as well as writing full documentation. BMI 2.0 also includes additional functions for describing variables and for working with structured and unstructured grids. For more information, see https://bmi.readthedocs.io.
If you're writing a BMI for a model, use BMI 2.0!