According to a support page on Google’s website, Google has revealed that its Pixel phones are guaranteed to receive Android updates for at least 2 years from when the device wa made available in the Google Store. It reads, “Pixel phones get Android version updates for at least 2 years from when the device became available on the Google Store. After 2 years, we can’t guarantee additional updates.”
Given that the Pixel phones were released in October, this means that come October 2018, there is no guarantee that you will continue to receive the latest Android updates. Before you fly into a rage, note that Google claims that they cannot guarantee additional updates. This does not mean that Google will no longer update the device, it’s just that after 2 years it is no longer a guarantee.
There could be a number of reasons such as hardware not being powerful enough to support the latest build of Android, or maybe Google has decided that they’d rather focus their resources on their new phones. So if you’re not the type to switch phones every 1 or 2 years, then this is something you should probably take into consideration.