# What are QUIC and HTTP/3? | SoftGlaze Browser glossary

> QUIC is the UDP-based transport under HTTP/3. How it speeds up connections, why it can bypass a TCP proxy, and why SoftGlaze turns it off for proxied profiles.

- Canonical URL: https://browser.softglaze.com/glossary/quic
- Last updated 2026-11-07

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[Proxies and networking](https://browser.softglaze.com/glossary?category=proxies-and-networking)

## QUIC and HTTP/3

Also called QUIC, HTTP/3, HTTP3, QUIC protocol, UDP

Definition

QUIC is an encrypted transport protocol that runs over UDP instead of TCP, and HTTP/3 is the version of HTTP that runs on it; browsers use them to load sites faster where the server supports them.

Last updated 7 November 2026

### How it works

HTTP/1.1 and HTTP/2 run over TCP with TLS on top. QUIC moves the transport to UDP and builds encryption, congestion control and multiple streams into it, which saves round trips and stops one lost packet holding up everything else. A server usually advertises HTTP/3 in an `Alt-Svc` header (or in DNS), and the browser switches to it for later requests if UDP gets through.

### Why it matters when you run several accounts

Most proxies a browser uses carry TCP only: an HTTP proxy tunnels TCP with `CONNECT`, and few SOCKS5 services relay UDP. If a proxied browser still tries HTTP/3, that UDP traffic has no path through the proxy. Depending on how the browser and network handle it, it either fails and falls back to TCP, or goes straight out from your own connection, which would show the site your real address.

### How SoftGlaze Browser handles it

HTTP/3 (QUIC) is disabled for every profile that has a proxy, so UDP cannot go around the proxy; the browser simply uses HTTP/2 or HTTP/1.1 through the proxy instead. A per-profile switch turns QUIC back on, which only makes sense on a proxy that genuinely carries UDP. Separately, WebRTC’s UDP traffic is kept off the direct path by the profile’s WebRTC mode.

### Sources

1.  [RFC 9000: QUIC: A UDP-Based Multiplexed and Secure Transport](https://www.rfc-editor.org/rfc/rfc9000) IETF
2.  [RFC 9114: HTTP/3](https://www.rfc-editor.org/rfc/rfc9114) IETF
3.  [Alt-Svc header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Alt-Svc) MDN Web Docs

Outside sources were checked in November 2026. Browsers, standards and vendors' pages change, so details that depend on them are as of that month.

### Related terms

-   [WebRTC leak](https://browser.softglaze.com/glossary/webrtc-leak) A WebRTC leak is when a page learns your real IP address through the browser's real-time communication feature, which gathers network addresses directly instead of through the proxy that carries the rest of your traffic.
-   [DNS leak](https://browser.softglaze.com/glossary/dns-leak) A DNS leak is when the lookups that turn site names into IP addresses go out through your own network and resolver instead of through the proxy or VPN, revealing which sites you visit and roughly where you are.
-   [SOCKS5](https://browser.softglaze.com/glossary/socks5) SOCKS5 is a proxy protocol that relays network connections of any kind between your device and a destination, with optional username and password authentication, and can pass the destination's hostname for the proxy to resolve.
-   [HTTP proxy](https://browser.softglaze.com/glossary/http-proxy) An HTTP proxy is a proxy that speaks the web's own protocol: the browser sends it ordinary HTTP requests, and for HTTPS asks it to open a tunnel to the site with the CONNECT method.

### Read more on this site

-   [Docs: at launch](https://browser.softglaze.com/docs/proxies#at-launch)
-   [Proxy pool](https://browser.softglaze.com/features/proxy-pool)

### See it in SoftGlaze Browser

Separate profiles, each with its own cookies, device values and proxy, on Windows. Try the app's screens in your browser first, or start the free trial; no card needed.

[Download for Windows](https://browser.softglaze.com/download) [Try the demo](https://browser.softglaze.com/demo) [All terms](https://browser.softglaze.com/glossary)