Hi,
In clang 13 I was happily using _ExtInt(256). It looks in clang 14 this has been replaced with _BitInt but the max width is only 128.
Yes, this is correct. _ExtInt was renamed to _BitInt by the C standards committee when accepting this type into C23. We intend to keep _ExtInt as an alias for the near-term.
As far as the new size limitation: unfortunately there are some significant problems with larger-than-128 bit _ExtInt/_BitInt types in our code-generation implementation (particularly around division/modulus operations on these types).
These are currently being worked on and we expect to be able to re-enable this in the near future, but in the meantime we don’t feel comfortable/able to permit these types until we are capable of supporting normal operations correctly.