This is not true, at least in my case.
My 2yr/unlimited contract technically ends 9/23/2015, yet AT&T reports that I am now eligible for upgrade.
Perhaps it's because my contract ends in September, rather than your October?
You might want to check further into your account. My contract date is 10/01/2015, and AT&T says I'm now eligible for an upgrade. However, when I click to see my upgrade options, I'm only eligible for a Next upgrade and I "may be eligible" for a 2-year contract upgrade on 10/01. Going to contact them today to try to get that date bumped so I can do the pre-order on Saturday.