The release of GCC 15.1 has introduced a significant change regarding union initialization in C and C++. Previously, using '{0}' was guaranteed to zero out the entire union, including padding bits. Now, it only initializes the first member to zero, potentially breaking compatibility with existing code that relies on full union zero-initialization. Developers are encouraged to use '{}' in C23 or C++ for complete union initialization or specify the option '-fzero-init-padding-bits=unions' to retain the old behavior. Additionally, while C++ Modules have been notably improved, further details on these improvements are needed for a clearer understanding of their implications.