How does key quota changes under concurrent requests

I am confused at how will key quota changes when more than one tyk gateway send request to an API at the same time, e.g. When 3 tyk gateways which was independently deployed send request to an API at the same time, how does the key quota behave? quota_remaining-1 or quota_remaining-3 ?
Thanks in advance!

It’s synchronised across the gateways, so -3