I'm not sure we're looking at the same thing.  I was talking about the docstring that shows up at the interactive prompt in response to 
>>> help(compile)

Going to hg.python.org/cpython and selecting branches, then default, then browse, got me to
http://hg.python.org/cpython/file/7010fa9bd190/Python/bltinmodule.c
which still doesn't mention AST.  I also don't see any reference to "src" or "dst", or any "source" that looks like it should be capitalized.

I agree that there is (to my knowledge, at this time) only one additional flag.  I figured ast or future was needed to get the compilation constants, so it made sense to delegate -- but you seem to be reading something newer than I am.