The Agiler router now speaks HTTP/3 over QUIC. Every project on the platform advertises it automatically, alongside the HTTP/2 and HTTP/1.1 it already serves. You do not need to turn anything on.
How a visitor ends up on HTTP/3
A browser cannot open an HTTP/3 connection the way it opens an HTTP/2 one. The transport underneath is different, so there is no ALPN negotiation to rely on. The server has to advertise the protocol first, and the router does that with an Alt-Svc header on every TLS response:
alt-svc: h3=":443"; ma=86400
The first request still arrives over TCP. The response carries the hint, the browser caches it for the advertised lifetime, and later requests go to QUIC on UDP port 443. No redirect, and no extra round trip on that first page load.
Clients without HTTP/3 support ignore the header and stay on TCP. So do clients on networks that block or degrade UDP: when the QUIC attempt fails, the browser falls back to HTTP/2 and stops retrying. Nothing about the existing path changes.
What QUIC changes
A lost packet only stalls its own stream. HTTP/2 multiplexes many requests over one TCP connection, and TCP hands up a single ordered byte stream. One dropped packet holds up everything queued behind it, including responses that already arrived complete. QUIC tracks each stream separately, so a retransmission delays only the stream that lost data. On a lossy mobile connection that is the difference between one slow image and a page that looks frozen.
Connections survive a change of network. TCP identifies a connection by source and destination address and port. Walk out of Wi-Fi range onto cellular, or sit behind a NAT that rebinds your port, and the connection is dead. QUIC uses a connection ID carried in the packets themselves, so it keeps going across the address change. Agiler’s edge passes QUIC through with its packet structure intact rather than terminating it, so this keeps working end to end.
The handshake is one round trip instead of two. TCP’s three-way handshake and the TLS handshake that follows it are separate exchanges. QUIC carries the cryptographic handshake inside its own. The saving is small in absolute terms and matters most on high-latency links.