HTTP/3 (QUIC)

HTTP/3 is an opt-in experimental feature on System.Net.Quic / MsQuic.

#pragma warning disable TWP001
proxyServer.EnableHttp3 = true;
#pragma warning restore TWP001

Prerequisites

• .NET 10+
• MsQuic:
  • Windows: in-box with the .NET runtime (Windows 11 / Server 2022+)
  • Linux: install libmsquic from packages.microsoft.com
  • macOS: not bundled; see the wiki for bundling notes
• System.Net.Quic.QuicListener.IsSupported == true before enabling
• Inbound endpoint: TransparentQuicProxyEndPoint or TransparentProxyEndPoint with EnableHttp3 = true

Dual-listen reverse (TCP + UDP)

Same IP:port speaks TLS H1/H2 over TCP and H3 over UDP, and can inject Alt-Svc:

#pragma warning disable TWP001
var proxy = new ProxyServer { EnableHttp3 = true, EnableHttp2 = true };

if (QuicListener.IsSupported)
{
    var reverse = new TransparentProxyEndPoint(IPAddress.Any, 443, decryptSsl: true)
    {
        EnableHttp3 = true,
    };
    proxy.AddEndPoint(reverse);
}
#pragma warning restore TWP001

CLI

listeners:
  - host: "0.0.0.0"
    port: 443
    decryptSsl: true
    enableHttp3: true

Full guide

Setup, macOS notes, Alt-Svc, bridges, and gap list: HTTP/3 wiki.