Do Google Play Game Service charge for request/time? Like Parse.com, they have something like 1000000 reg/day is free and will charge the developer for anything more than that. What is Google Play's part for that? I could not find any of the documentation on that part online.
After sign up the Google Play Game Developer program and playing around for a while. I believe it is not entirely free per say.
In Google API console, there is a section that you can check your APIs that link to your game/app that created in Google Play Game Console(This is the different console from the former). There you can check the APIs' quota and limit. However, it is rather high. For Google Play Game Service, it is 50 millions requests per day, which, if your game can reach that, I believe you won't mind paying.
Google Play Gaming Services are free and doesn't have any limit for any number of concurrent users. The aim of the service is to provide tools at par with Apple's GameCenter. Since GameCenter is free, GPG service is free too.
PS: Doesn't this question belong on SO? Just asking.