HTTP 2 vs HTTP 3 — What's the Difference?

Mike's Notes

Useful background information.

Resources

• https://blog.levelupcoding.com/
• https://www.linkedin.com/posts/nikkisiapno_http-2-vs-http-3-whats-the-difference-activity-7307711303282802688-xgWK/
• https://en.wikipedia.org/wiki/HTTP
• https://httpwg.org/specs/

References

• 
  

Repository

• Home > 

Last Updated

23/03/2025

HTTP 2 vs HTTP 3 — What's the Difference?

By: Nikky Siapno

Level Up Coding: 23/03/2025

HTTP 1 started in 1996. The very next year HTTP 1.1 followed. It was another ~20 years until HTTP 2 became standardized in 2015. And in recent years (2022), HTTP 3 was officially standardized.

But what’s the difference?

Starting at the foundation:

HTTP 1.1:

• Persistent connections — Reuses connections instead of opening new ones
• Chunked transfers — Sends data in parts instead of waiting for the full response
• Improved caching — Introduced headers for better caching and connection management
• Sequential requests — Requests block each other (HoL blocking at the request level)
• Multiple connections needed — Browsers used multiple TCP connections for speed
• It introduced core features still used today.

HTTP 2:

• Multiplexing — Multiple requests in a single TCP connection
• Header compression (HPACK) — Reduces metadata size
• Stream prioritization — Ensures critical resources load first
• Head-of-line (HoL) blocking — A lost packet blocks all streams
• While HTTP 2 optimized TCP, it remained constrained by TCP’s head-of-line blocking.

HTTP 3:

• Built on QUIC (UDP) — No more TCP bottlenecks
• Independent streams — Packet loss in one stream doesn’t affect others
• Faster handshakes — Combines transport + encryption setup in one step
• Mandatory encryption (TLS 1.3) — Security by default
• Connection migration — Seamless across network changes

In a nutshell: HTTP 2 optimized TCP, but HTTP 3 rewrites the game with QUIC, making it faster, more reliable, and encrypted by default.

Which fact surprised you?