Google has the Support document for guaranteed Android and security Updates to the Pixel and Nexus Smartphones as revised. Accordingly, the Nexus 6P (Test) and the Nexus 5X (Test) is now two months longer with security Updates. From September 2018, has become in the revised version of November 2018.
The information in the document, describe, until when Google guarantees Updates. This does not mean that then no Updates will be more spread out, as is happening now. In addition to the extended Support for security Updates, Google for the Nexus 6 and Nexus 5X now until November 2018, phone and Online Support.