Are you still partying like it’s 1999 on a 32-bit browser? Pshaw! To borrow a line for Weird Al Yankovic, “What kinda chip you got in there, a Dorito?” Well, Google is having none of it. Users running Chrome on a 64-bit Windows system with at least 4GB of RAM installed will be migrated from 32-bit to 64-bit, so long as they have Chrome configured

Source: Hot Hardware – Google Chrome 58 Will Automatically Migrate Supported Users To 64-bit Branch