I also believe that, at some point, Ruby _will_ support RBS/steep format in the source code, but the advantage to something like .rbs files is that projects tha

I also believe that, at some point, Ruby _will_ support RBS/steep format in the source code, but the advantage to something like .rbs files is that projects that need to support 2.x and 3.x don’t have to maintain two different versions of the code.