Before a Pixel 2 and 2 XL, Google had a robe of earnest a Nexus and Pixel inclination Android chronicle updates for dual years, though confidence fixes for three. That changed with a second-generation Pixels, that were guaranteed both forms of updates for 3 years. The Pixel 3 family will advantage from a same courtesy.
If we buy a Pixel 3 or 3 XL, you'll be happy to know that Android chronicle and confidence updates are guaranteed until Oct 2021, 3 years from now. If Google continues a yearly cycle of Android releases, that means you'll expected get Android Q, R, and S, before a guarantee expires.
While this isn't iPhone-level support, it's positively improved than a dual year deadline. We're blissful to see that 3 years of updates are now apropos a normal for Google's Pixels.