[temac]

On the contrary one of the reason of COM is to not depend on the C++ ABI, which is not stable at all under Windows (it has been de-facto stable for the three last version of MSVC, but was broken each time before, and the recent stable stride is not an indication this ABI compat will continue - actually it is well known that MS internally maintains an ABI incompat version of the STL that will be very probably used in the future, to fix some issues and optimize things)

On another platform, libstdc++ is mostly backward compatible, within reason.

The C++ standard is not "officially" concerned by stability, except that in practice people in the committee care a lot (because some major implementations care a lot) so some modifications are rejected because they would break the ABI currently used in practice.

[ChrisSD]

In regards to COM I was specially thinking about how virtual functions and methods are layed out. This cannot change without breaking a lot of code. Already this causes issues in non-C++ languages (e.g. the difference with thiscall in C++).

[quotemstr]

The vtable layout is much smaller and much more stable than C++ as a whole. COM has a ton of value.

[pjmlp]

And it got even better with the UWP changes.

[ncmncm]

You don't get a stable ABI by accident. MS chose to maintain stability on these recent releases. This is a change from past practice, in response to customer needs.

Customers who needed stability were staying on ancient compilers. MS probably would rather have them using new versions, and exercising new features.