Sorry, I wasn't trying to imply the new libstdc++ wouldn't work with old code, just explaining to the poster why the new ABI is required in the first place. The

Sorry, I wasn't trying to imply the new libstdc++ wouldn't work with old code, just explaining to the poster why the new ABI is required in the first place. The changes to libstdc++ which are incompatible are what is causing the dual ABI to be required - And of course, the dual ABI is what allows old programs to continue to use the old ABI with a newer libstdc++ library without problems.