1xx Informational
Informational responses indicate that the request was received and understood. It is issued on a provisional basis while request processing continues. It alerts the client to wait for a final response.
100
Continue
The initial part of the request was received; the client should proceed with sending the body.
101
Switching Protocols
The server accepts the request to upgrade the connection to a different protocol.
102
Processing
The server has received and is processing the request, but no response is available yet.
103
Early Hints
Allows the server to send Link headers before the main response, prompting the browser to preload assets.