alt-svc: h3=":443" is an advertisement, not a completed HTTP/3 connection. It says that a client may try the origin over HTTP/3 at UDP port 443. A useful acceptance check must also prove that the client supports HTTP/3, QUIC reaches the selected endpoint, TLS and HTTP negotiation finish, ...

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Last edited on August 13, 2026

August 13, 2026 No Comments