QUIC

QUIC is a transport protocol that runs over UDP and was designed to fix long-standing limits of TCP plus TLS. It folds the connection and encryption handshakes together, so a session can start in fewer round trips, and it carries multiple independent streams at once without the head-of-line blocking that stalls all streams on a single TCP connection when one packet is lost. Encryption is built in rather than layered on top, and connections can survive a network change, making QUIC well suited to mobile.

QUIC is the foundation of HTTP/3, which is why modern web traffic increasingly rides on it. For proxying, QUIC's use of UDP matters: an HTTP proxy built around TCP CONNECT does not carry it, and only a proxy that relays UDP can. The s4m SOCKS5 proxy relays TCP and UDP, while the device-wide VPN tunnels all traffic including QUIC. If a tool insists on QUIC and your proxy is TCP-only, either force it back to TCP/HTTP2 or route it through the VPN instead.

For proxying, QUIC's reliance on UDP is the practical catch: an HTTP proxy built on TCP CONNECT cannot carry it, while a UDP-capable SOCKS5 proxy or the device-wide VPN can. The s4m SOCKS5 endpoint relays UDP, and the VPN tunnels everything. If a tool insists on QUIC and your path is TCP-only, either force it back to HTTP/2 over TCP or move that traffic to the VPN so the UDP flow has somewhere to go.