When intro APR expires, at one point does interates start to accrue?

So I have a BoA credit card with 0% intro purchase rate for the first 9 billing cycles. The 9th billing cycle cut on 9/9/2016, and the payment due date is 10/4/2016

So my question is, in order to avoid paying interests, do I have to pay off the balance by 10/4/2016?

Or, does the balance then get subjected to the grace period on the October bill, meaning I have until 11/4/2016 (or whenever the Nov due date is) to pay it off?