Google Cloud Messaging - Sending a message to many users?

Question

Android

I compare two pages:
https://developers.google.com/cloud-messaging/http...
https://developers.google.com/cloud-messaging/noti...
One shows that the notification_key is outdated and to send message to many clients, you need to use registration_ids, where you can push up to 1000 recipients.
Bottom of the page: Updated December 16, 2015
The second one says that notification_key is used and groups of max 20 users are registered.
Updated January 14, 2016
Where is the truth? I need to send a lot of pushes and 20 is not enough.
If the first option is correct, can you show an example to send? In this case, what should be written in the to parameter if it is required, when the entire list will be in registration_ids?

Answer 1

If the task is to send a push to all users, then it seems to me that this solution will be more logical: https://developers.google.com/cloud-messaging/topi...
"Create" a topic, subscribe a client to it and send pushes