C++20 introduced a breaking change where u8 string literals changed from const char arrays to const char8_t arrays, causing previously compatible code to fail compilation. This violates the common assumption of backward compatibility across C++ versions, and Google's style guide recommends avoiding the u8 prefix to mitigate migration issues.
Coost v4.0.0 is a major release that raises the minimum C++ standard to C++17, removes high-maintenance modules (dynamic libraries, hooks, HTTP/SSL components, fastring, fastream, and coroutine channels), and adds support for Windows ARM64 and FreeBSD platforms. Core components have been optimized and consolidated into the co namespace with improved APIs and performance improvements across logging, closures, synchronization primitives, and other utilities.