No longer used. Originally meant "Subsequent requests should use the specified proxy."
What does HTTP 306 mean?
The 306 Switch Proxy code is part of the 3XX class. This is a redirection code — the client must take further action, usually following a new URL.
When is it used?
A server returns 306 Switch Proxy in situations matching the definition above. You will encounter it inspecting network requests, reading logs, or testing an API. Whether it signals a problem depends on its class: 2xx and 3xx are normal, while 4xx and 5xx usually need attention on the client or server respectively.