HTTP/2 push is no longer supported by Chrome web browser. Other browsers may discard it at some point. With such browsers, HTTP/2 push will be disabled, therefore using this feature is safe but it will have no effect. On the other hand, this feature is not deprecated and generally it is still allowed to use it, so feel free to opt-in this annotation to eliminate this warning, if you are sure that you need it. For example, it makes sense to use with a non-browser client that for sure supports HTTP/2 push.