Glossary · Performance

HTTP/2

HTTP/2 is the second major HTTP version, multiplexing many requests over one connection with header compression to load pages faster than HTTP/1.1.

Updated October 5, 2026

HTTP/2 (RFC 9113) is a binary version of HTTP that carries many concurrent requests and responses, called streams, over a single TCP connection. It keeps the same methods, status codes and headers as HTTP/1.1; only the transport format changes.

Why it matters

HTTP/1.1 needed multiple connections and workarounds like domain sharding and file concatenation to load many assets in parallel. HTTP/2 removes that need through multiplexing, and shrinks repeated headers with HPACK compression. Browsers use it only over TLS, negotiated through ALPN during the handshake. One limitation remains: because it runs on TCP, a single lost packet stalls all streams (head-of-line blocking), which HTTP/3 addresses.

Example

Check what a server negotiates:

curl -sI --http2 https://example.com | head -n 1
# HTTP/2 200

Enabling it in nginx:

listen 443 ssl;
http2 on;

On older nginx versions, the directive is listen 443 ssl http2;.

Common mistakes

  • Still concatenating all files and sharding domains, which wastes the benefits of multiplexing.
  • Assuming it is on because HTTPS is. Check the actual protocol in a response.
  • Forgetting that a proxy or CDN may speak HTTP/2 to browsers but HTTP/1.1 to your origin.
  • Expecting server push to help. Browsers have dropped support for it.

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