Which assembly? Assembly with macros? Assembly with synthetic instructions?

If you use

    mov %i0, %l0

instead of

    or %g0, %i0, %l0

Then that isn't "the lowest level you can target."

I was thinking of x86 when I wrote that, also I am not sure macros count as an abstraction level since they are just preprocessors?

What I meant to say is that since there is no way to directly write microcode, assembly is the lowest level software can target.

Yes and no, you can use c in situations where there's no "assembly", for instance when synthesizing FPGAs. You target flow graphs directly in that case IIRC.