To be clear, there is ONE, SMALL API change. In versions >= 0.4.0 the function px_proxy_factory_get_proxies() may return NULL. Applications that didn't consider this case should be fixed regardless. Apps that do consider this case will work on both versions. libproxy 0.4.0 does include a soname bump, so applications will probably need to be rebuilt. Applications using any of the bindings should not need a rebuild.
To be clear, there is ONE, SMALL API change. In versions >= 0.4.0 the function px_proxy_ factory_ get_proxies( ) may return NULL. Applications that didn't consider this case should be fixed regardless. Apps that do consider this case will work on both versions. libproxy 0.4.0 does include a soname bump, so applications will probably need to be rebuilt. Applications using any of the bindings should not need a rebuild.