101 Switching Protocols
Meaning
The server is switching protocols as requested by the client via the Upgrade header.
When to Use
When agreeing to switch to a different protocol (e.g., switching to WebSocket after an Upgrade request).
Example
Client requests upgrade to WebSocket with HTTP, server responds with 101 to confirm protocol switch.
When Not to Use
Do not use if no protocol change is being performed.
Source
RFC 9110