1xx Informational

A provisional response signaling that the request was received and processing is continuing. It is sent before the final response.

100ContinueThe server received the request headers and the client should proceed to send the request body.101Switching ProtocolsThe server agrees to switch protocols as requested by the client via the Upgrade header.102ProcessingThe server has received and is processing the request, but no response is available yet. Deprecated.103Early HintsSends preliminary Link headers so the client can start preloading resources before the final response.