The OS build number (for example, “NJH47F” or “OPM4.171019.021.D1” on Android) has been removed from the user-agent identification (User-Agent header and navigator.userAgent) on Android and on iOS. The iOS change follows Safari's implementation and freezes the build number as "15E148" instead of removing it. This will prevent abuses of that information such as exploit targeting and fingerprinting. It'll also bring Chrome closer in line with RFC 7231 section 5.5.3.