HTTP/3

HTTP/3 is the newest version of the web's protocol, and its defining change is the transport underneath: it runs over QUIC and UDP rather than TCP. This removes the head-of-line blocking that affected HTTP/2, where one lost packet stalled every stream on the connection; with QUIC, streams are independent. It also inherits QUIC's faster, encrypted handshake and its ability to survive a network change, which together make HTTP/3 quicker to start and more resilient, especially on mobile.

The move to UDP has a practical consequence for proxying: because classic HTTP proxies and the CONNECT method only carry TCP, HTTP/3 cannot pass through them. It needs a path that relays UDP — a SOCKS5 proxy that supports UDP, or a device-wide VPN that tunnels everything. If a client attempts HTTP/3 through a TCP-only proxy, it will typically fall back to HTTP/2 over TCP. When you specifically need HTTP/3, route it through the s4m VPN or the UDP-capable SOCKS5 endpoint rather than the HTTP proxy.

Because HTTP/3 needs a UDP path, it cannot cross a classic HTTP proxy's TCP-only CONNECT tunnel; a client will usually fall back to HTTP/2 over TCP. When you specifically need HTTP/3, route it through a UDP-capable SOCKS5 proxy or the device-wide s4m VPN. For most tasks the fallback is fine and invisible, so only reach for a UDP-capable path when a tool genuinely requires QUIC rather than accepting the TCP fallback.