According to the information on WhatsApp FAQ section, Android phones running on Android 2.3.7 operating system and lower as well as iPhones running on iOS 8 and lower will not be compatible with the chat app in a week from now. However, the instant messaging platform will keep the app running for select phones with KaiOS 2.5.1+ OS, including JioPhone and JioPhone 2. Notably, WhatsApp also stressed on the fact that these older versions of Android and iOS operating systems “can no longer create new accounts, nor re-verify existing accounts after February 1, 2020.”
Here is the list of all the operating systems that will not support WhatsApp from 1st Feb:
-Android versions 2.3.7 and older
-iOS 8 and older
-All Windows OS phones from 31 December 2019

WhatsApp also listed the operating systems that the app will support:
-Android running on OS 4.0.3+
-iPhone running on iOS 9+
-Select phones running on KaiOS 2.5.1+, including JioPhone and JioPhone 2