[addaon]

> they produced the next version of unextensible shit so now int128 can't be added

It's hard to think of something more "added" (or, for that matter, more "extensible") than `_BitInt(128)`.

[mike_hock]

It has been tacked on as a "totally not an integer" type because the integer system isn't extensible enough to accommodate it.

It could of course be added with an ABI break (bumping intmax_t to int128), but that's not being done because it would be an ABI break. Hence, not extensible in practice.