Google confirms Nexus 5X and Nexus 6P will not be updated to Android P
As a “bonus,” customers who own a Pixel C tablet should not hope to get the update since Google is not going to offer any Android OS upgrade going forward. While we can't say the news comes as a surprise, it's a pity that such popular phones like these Nexuses stop being supported by the maker.
On the bright side, Google will continue to provide Nexus 5X and Nexus 6P owners with monthly security updates until at least November 2018. After Google will no longer offer these security patches, you'll probably have to upgrade to a newer phone.
In the meantime, you can now flash the newly released Android P Developer Preview 1 if you own one of the Pixel smartphones, i.e. Pixel, Pixel XL, Pixel 2, and Pixel 2 XL.