# HTTP/1.1 Upgrade header

> header field introduced in HTTP/1.1; in the exchange, the client begins by making a cleartext request, which is later upgraded to a newer HTTP protocol version or switched to a different protocol; connection upgrade must be requested by the client

**Wikidata**: [Q5636136](https://www.wikidata.org/wiki/Q5636136)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/HTTP/1.1_Upgrade_header)  
**Source**: https://4ort.xyz/entity/http-1-1-upgrade-header