Google's Nexus Support page has been updated with the Pixel's Android version update information.
As stated on the page, the Pixel phones will be guaranteed for at least 2 years of Android version updates starting from the date when the device became available on the Google Store. Which for Pixel's case, after October 2018, there would be no guarantee for additional updates.
Meanwhile, Google will continue to provide security patches for at least 3 years from the date when the device became available in the Google Store or at least 18 months from the date of the sales discontinuation, whichever is longer.
While Pixel is similar with Nexus, but they are being branded and marketed differently in order to achieve a wholly different grand vision, but Pixel should deserve their own URL though.
Personally, I believe Google should step up their game in the version updates, consider that Pixel phones are sold as premium devices, they should have at least cover 3 years of version updates instead of 2 years.