The smartphone market has a very high turnover rate. The commonly established, or at least expected, practice is to support a device for two years after its launch. Of course, that still depends on the OEM and whether said OEM makes an explicit promise. Google just put that promise down on writing when it updated its "end-of-life" support page with an entry for its Google Pixel. Despite being Google's special smartphone, it isn't getting any special treatment and is guaranteed only two years' worth of Android version updates.