“服务器不支持，或者拒绝支持在请求中使用的HTTP版本。这暗示着服务器不能或不愿使用与客户端相同的版本。响应中应当包含一个描述了为何版本不被支持以及服务器支持哪些协议的实体。“ — wikipedia

“The server does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client. The response SHOULD contain an entity describing why that version is not supported and what other protocols are supported by that server.“ — ietf