XQUIC is a production-grade C implementation of the QUIC transport protocol (RFC 9000) and HTTP/3 (RFC 9114), developed by Alibaba. It provides a full-featured QUIC stack including connection management, packet encryption, loss detection, congestion control (BBR, CUBIC, NewReno, Copa), and HTTP/3 with QPACK header compression. The library also supports experimental extensions such as Multipath QUIC, Forward Error Correction (FEC), and Media over QUIC (MoQ) for streaming media. The architecture is modular with a callback-driven engine, pluggable congestion control and TLS backends (BoringSSL, BabaSSL), and extensive testing infrastructure including unit tests (CUnit), integration shell scripts, and interoperability tests. The codebase is well-structured with reusable utility components (ring buffers, hash tables, object pools, timer managers) and demonstrates strong software engineering practices, though the large number of feature flags and experimental extensions introduce some complexity and potential drift.