While /rest/v1/stats/usage.json can return API usage from different API users over the course of the day, there's no way today to see a subscription's daily request limit (enforced or purchased). As a result, if you wanted to scale a program to use a certain ratio of calls relative to the subscription, you must first retrieve the number in the UI.
Having API access and exposure to the request limit in addition to daily calls would be a major win for Marketo integration developers, as proper scales and checks could be dynamically built into applications.
.png)