Static and Rotating Proxy IPs
Tell a fixed proxy endpoint from a fixed exit address, and distinguish manually changing list entries from a service that rotates exits.
A static proxy endpoint can sit in front of rotating exit addresses. When a service promises a fixed or changing IP, find out whether it means the address entered into your client or the outbound address seen by the website.
Who selects the next address?
Choosing a different entry from a free proxy list and configuring the client again is client-controlled switching. An application needs its own selection logic to cycle through a downloaded list.
A rotating service can instead keep one connection endpoint and select exits behind it. Rotation might happen per request, per connection, after a time interval, or according to a named session. The distinction matters when a client reuses connections. An address change also does not clear an application session.
What needs to stay stable?
A server that allowlists source IPs needs the outbound address it will actually observe. A stable proxy hostname is insufficient. Changing the endpoint is also no guarantee of a different exit: both endpoints may share an outbound network.
For troubleshooting, record the configured endpoint alongside the exit observed at the destination. curl's connected-peer information describes its own connection, which is not a separate observation of the destination-side exit.
Repeated requests show the behavior during those requests. A continuing address policy must come from the service's terms; an unchanged address in a public list offers no availability promise.