API Gateway Boto3 get_usage() - Running Total or just daily?

Hi all - writing a quick lambda to get usage per API key so we can run that by billing when the time comes. Stupid question, but just want to make sure...

I know the response from boto3's apigateway client looks like this:

values: {
   'api key id':{ [
         [ usage, remaining ],
         [ usage, remaining ], 
         ...
     ]
   }
}

is the usage for each a running total, or per day? the docs for this word it as though it's just per day, but the example response makes it seem like it's a running total....

{..., "values" : 
    { "{api_key}" : [ 
         [0, 100], 
         [10, 90],
         [100, 0]
         ]
     }

either way is fine, but obviously it'll matter from a billing perspective :)

thanks in advance!