While a two-year old smartphone isn’t exactly what you would consider “old” in terms of usability and features, as far as OEMs are concerned, such devices are typically viewed as “ancient” and it isn’t often that we see OEMs support devices that are older than two years. Google is no different but the good news is that at least Pixel/Nexus owners have an expiry date to look forward to.
Google has recently published updated timeframes on its website in which they indicate when support and updates for its Pixel and Nexus devices will end. Starting with the Nexus, owners of the Nexus 6P and Nexus 5X can expect that Android version updates will no longer be guaranteed after September 2017, and that there will also be no guaranteed security patch updates after September 2018.
As for the Pixel and Pixel XL, Google says that there will be no guaranteed Android version updates after October 2018, and no guaranteed security patches after October 2019. Note that Google’s wording says that there is no guaranteed updates, meaning that while there is a chance that the Pixel and Pixel XL could see an update to 2019’s Android, it is not a guarantee that it will.
We suppose this is normal especially given the nature of carrier contract lengths in which users are usually given options to upgrade to a newer handset, sometimes even after the first year.