I would have expected to be a bug in the documentation? Why would they turn FMA off for standard compliant C mode, but not for standard compliant C++ mode?

But the documentation does appear to be correct: https://godbolt.org/z/3bvP136oc

Crazy.

it defaults to off for standard-compliant mode. Which in my mind was the default mode as that's what we use everywhere I have worked in the last 15 years. But of course that's not the case.

In any case, according to the sibling comment, the default is 'fast' even in std-compliant mode in C++, which I find very surprising. I'm not very familiar with that corner of the standard, but it must be looser than the equivalent wording in the C standard.