One of the constant hot topics in the Android world is that of updates. Whether they be major updates or just routine security fixes, when a device will be updated to the latest version of Android is always a highly debated point. The general consensus is that most smartphones will receive updates for two years from launch. If you own a Nexus device in particular, then not only are you guaranteed the two-year update cycle, but your device is considered likely to receive those updates extremely soon after they become available. Speaking of which, Google is now listing what is essentially a software update end of life time-frame for Nexus devices.
To get to the important bit, in terms of what should be expected for the lifespan of updates for current Nexus device owners, the support page notes that as of October of this year, the Nexus 9 will no longer be automatically eligible for updates. While the two current Nexus smartphones, the Nexus 5X and Nexus 6P will both see their guaranteed support coming to an end in September 2017. The support page also does note the devices which have essentially already passed their guaranteed update cycles like the Nexus 5 whose support ended in October 2015 or the Nexus 7 (2013) with its date listed as July 2015. Going back a little further and the Nexus 10 which saw its automatic update support expiring in November of 2014. Strangely, devices like the Nexus 6 and the Nexus Player are not listed, although it is presumed that both will continue to see their updates for two years and therefore their likely expiration date will be in and round the date listed for the Nexus 9.
Of course, it is worth remembering that these time-frames relate to software updates. As such, if you do own a Nexus device and as it nears its software update expiration date, the device will continue to receive security fixes for about an additional year. So while you might not receive the latest version of Android, you will still be protected from the various security issues that surface in the year following the end of software updates for the device. Not to mention, these dates are not to say that a certain Nexus device will definitely not receive updates after their respective dates, as the dates are only relating to when they are not guaranteed to receive Android software updates.