While there are some devices that are now with a few 18-month warranty periods, Google's spend up to two years. In that period, a Nexus device like the 5X, manufactured by LG, has two years in which it will receive updates to Android. After that time frame, you will only be able to receive critical security updates.
But to make everything clearer, now, from the Google support page the owners of a Nexus device they will know exactly until when your device will be able to receive these updates to keep the system up to date. An interesting information for the owners of a Nexus and thus really stick to the exact period in which they will be able to receive these new versions such as Android N this summer or the next ones that arrive.
Google has published a table that lists the month in which Nexus devices will not receive any more updates of Android. Both the Nexus 5X and Nexus 6P are guaranteed to receive Android updates until September 2017, while the Nexus 9, which recently ceased production, has a deadline of October 2016. Meanwhile, the Nexus 5 ended its warranty period in October 2015, the Nexus 7 (2013) ended in July 2015 and the Nexus 10 ended in November 2014.
And although these months end the warranty period for Android updates, it is possible that some may receive updates to Android after that second year. Interesting information shared by Google and thus make things clear so as not to lead to confusion. Apart from the fact that they will receive security patches up to 3 years after their launch or 18 months after they were removed from the Google Store.
Anyway, you can always opt for ROMs custom which is in the Nexus where they take more entity. My Nexus 7 from 2012 was able to update it to Android 6.0 Marshmallow thanks to a developer of this type of ROMs, so the life is lengthened for a device that exceeds 4 years of life.