50 API calls/secondis based on single user or all the users?

Hi there,
I know many have asked this question but i just want to be clear about
Is 50 API calls/second limitis based on single user (where a single user can make 50 max requests) or all the users? Lets say im an inde-developer and have over 1 million active users then current pricing structure where 50$/10 extra call will be something not affordable for me.
Please advise

The free limit is 50 req/sec per application (all users)