426 Upgrade Required 是一种HTTP协议的错误状态代码，表示服务器拒绝处理客户端使用当前协议发送的请求，但是可以接受其使用升级后的协议发送的请求。
服务器会在响应中使用 Upgrade 首部来指定要求的协议。
426 Upgrade Required
HTTP/1.1 426 Upgrade Required Upgrade: HTTP/3.0 Connection: Upgrade Content-Length: 53 Content-Type: text/plain This service requires use of the HTTP/3.0 protocol
| Specification | Title |
|---|---|
| RFC 7231, section 6.5.15: 426 Upgrade Required | Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content |
AcceptAccept-CharsetAccept-EncodingAccept-LanguageAccept-RangesAccess-Control-Allow-CredentialsAccess-Control-Allow-HeadersAccess-Control-Allow-MethodsAccess-Control-Allow-OriginAccess-Control-Expose-HeadersAccess-Control-Max-AgeAccess-Control-Request-HeadersAccess-Control-Request-MethodAgeAllowAuthorizationCache-ControlConnectionContent-DispositionContent-EncodingContent-LanguageContent-LengthContent-LocationContent-RangeContent-Security-PolicyContent-Security-Policy-Report-Only [我来译!]Content-TypeCookieCookie2DNTDateETagExpectExpiresForwardedFromHostIf-MatchIf-Modified-SinceIf-None-MatchIf-RangeIf-Unmodified-SinceKeep-AliveLarge-Allocation [我来译!]Last-ModifiedLocationOriginPragmaProxy-AuthenticateProxy-AuthorizationPublic-Key-PinsPublic-Key-Pins-Report-Only [我来译!]RangeRefererReferrer-PolicyRetry-AfterServerSet-CookieSet-Cookie2SourceMap [我来译!]HTTP Strict Transport SecurityTETk [我来译!]TrailerTransfer-EncodingUpgrade-Insecure-RequestsUser-AgentVaryViaWWW-AuthenticateWarningX-Content-Type-OptionsDNS 预读取X-Forwarded-ForX-Forwarded-HostX-Forwarded-ProtoX-Frame-Options 响应头X-XSS-Protection100 Continue101 Switching Protocol200 OK201 Created202 Accepted203 Non-Authoritative Information204 No Content205 Reset Content206 Partial Content300 Multiple Choices301 Moved Permanently302 Found303 See Other304 Not Modified307 Temporary Redirect308 Permanent Redirect400 Bad Request401 Unauthorized403 Forbidden404 Not Found405 Method Not Allowed406 Not Acceptable407 Proxy Authentication Required408 Request Timeout409 Conflict410 Gone411 Length Required412 Precondition Failed（先决条件失败）413 Payload Too Large414 URI Too Long [我来译!]415 Unsupported Media Type [我来译!]416 Range Not Satisfiable417 Expectation Failed426 Upgrade Required [我来译!]428 Precondition Required429 Too Many Requests431 Request Header Fields Too Large [我来译!]451 Unavailable For Legal Reasons [我来译!]500 内部服务器错误501 Not Implemented502 Bad Gateway [我来译!]503 Service Unavailable [我来译!]504 Gateway Timeout [我来译!]505 HTTP Version Not Supported [我来译!]511 Network Authentication Required [我来译!]CSP: base-uri [我来译!]CSP: block-all-mixed-content [我来译!]CSP: child-src [我来译!]CSP: connect-src [我来译!]CSP: default-src [我来译!]CSP: font-src [我来译!]CSP: form-action [我来译!]CSP: frame-ancestors [我来译!]CSP: frame-src [我来译!]CSP: img-src [我来译!]CSP: manifest-src [我来译!]CSP: media-src [我来译!]CSP: object-src [我来译!]CSP: plugin-types [我来译!]CSP: referrer [我来译!]CSP: report-uri [我来译!]CSP: require-sri-for [我来译!]CSP: sandbox [我来译!]CSP: script-src [我来译!]CSP: style-src [我来译!]CSP: upgrade-insecure-requests [我来译!]CSP: worker-src [我来译!]