Google has officially laid out exactly when customer support will end for Pixel and Nexus devices. Essentially, as long as a device continues to receive security updates, it will continue to receive support over the phone and online from Google. Device OEMs are only required to keep major Android updates coming for 18 months after a device is released, but Google provides major updates to Nexus and Pixel devices for at least two years, usually allowing them to see two major Android version upgrades beyond the one they were released with. Security updates, on the other hand, normally continue for far longer. Nexus and Pixel devices get guaranteed updates for one year after major update support ends. The dates revealed by Google correspond to when guaranteed support will end for a given device, but Google and the device manufacturer can continue to offer updates and support after that date if they wish to.
The earliest current device to see its support end is the Nexus 6, which will see guaranteed security updates and support end this October. October of last year marked the end of guaranteed major updates for the device. All older models, such as the popular Nexus 5, have already hit the end of the support road. The Nexus 9 shares its support dates with the Nexus 6. The Nexus 5X and Nexus 6P, on the other hand, will see major updates end this September, and security updates and support end in September of 2018. The Pixel and Pixel XL will see their guaranteed major updates come to an end in October of 2018, then guaranteed security updates and support will end one year later.
A couple of Nexus and Pixel devices are missing. The Pixel C is notably absent from the listing, but since it was released in December of 2015, it's a safe bet that it will stop getting major updates in December of 2017, then stop getting security updates in December of 2018. The Nexus Player was released in November of 2014, meaning that it will stop getting security updates this November. No other devices were listed by the Alphabet-owned company as Chromebooks, Android One devices, and other such Google-supported products are all on different update schedules to its smartphones.