I agree. I happened to see Boris' tweet about it as soon as it posted, and the endpoint for redeeming the credits (the one that fires when you click it on the usage page) was already returning sporadic 400s for everyone.

I wouldn't be surprised if they pulled it back so they could spread out the load.

edit: whoops, meant to leave this as a reply to the (now-sibling) comment from 'flutas.

Yeah, same here. I think it's just rolling out gradually, mine wasn't showing for the longest time then just randomly appeared.