Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
HTTP/1.1 Upgrade header
open-in-new
<p>The Upgrade header field is an <a href="/facts/List_of_HTTP_header_fields/hEkcQe2f">HTTP header field</a> introduced in <a href="/facts/HTTP%2f1.1/TWtvf7JD">HTTP/1.1</a>. In the exchange, the client begins by making a <a href="/facts/Cleartext/tWnBDCgE">cleartext</a> request, which is later upgraded to a newer <a href="/facts/HTTP/TWtvf7JD">HTTP</a> protocol version or switched to a different protocol. A connection upgrade must be requested by the client; if the server wants to enforce an upgrade it may send a 426 Upgrade Required response. The client can then send a new request with the appropriate upgrade headers while keeping the connection open. </p>