Hi there! The Unlimited Gigs plan comes with Unlimited Talk, Text and Data up to 35GB. After that, Quality of Service (QoS) kicks in. Customers who use more than 35GB of data during a billing cycle will be deprioritized during times and places where the network is constrained. You may experience some periodic slowed data speeds while in an area that has a high volume of data traffic on the network. Once network resources are no longer constrained or you move to a non-constrained location, your data speed returns to normal. Quality of Service is not the type of throttling you may be familiar with, which is when you hit the applicable data threshold, your wireless data speed is reduced for their entire cycle, 100% of the time, no matter where you are. 35GB is a ton of data, far more than most customers ever use, so we take steps to protect our customers from heavy data users that use more share of the network. We do however, try to minimize the impact even to our heaviest users. We take action only when your current cell site is congested.
I have personally tested this issue to see how well "Unlimited" stands up.
What the Agent stated is correct, that after 35 GB, your data may be slowed and only when the cell site is congested. I have used data in well excess of 35GB and than at various times of the day and throughout my city (Las Vegas, Nevada) performed data speed tests on Band 26 and Band 41 of LTE. While I can't speak for other geographical areas other than Las Vegas,
Some cell sites based on overall congestion (pre-35GB allottment) tested with slow data speeds. Post-35GB tests revealed that approximately 90% of the time no actual speed throttling occurred. In fact, Post-35GB speed tests on some sites exceeded 80Mbit speeds and on one occasion exceeded 100MBit (see image below).
So all in all, I would not be worried about the QoS (Quality of Service) deprioratization. No other carrier has such a liberal data usage policy, which is why I continue to use Boost.