For libcxx & libstdc++ yes correct. Clang, however, does strive to maintain compatibility with G++. So you can build a library with clang & use it from g++. It

For libcxx & libstdc++ yes correct. Clang, however, does strive to maintain compatibility with G++. So you can build a library with clang & use it from g++. It strives, and for the most part achieves, to be a drop-in replacement for GCC, which includes ABI compatibility.