On its website, WhatsApp confirms that it now only supports the following devices:

Android running OS 4.0.3+

iPhone running iOS 9+

Select phones running KaiOS 2.5.1+, including JioPhone and JioPhone 2

Some older operating systems which will continue to receive support for a limited time. The app will continue to work on devices running Android 2.3.7 and older or iOS 8 and older until February 1st, 2020. However, WhatsApp will no longer be supported on the Windows Phone operating system from December 31st, 2019.

WhatsApp warns that features of the app may stop working at any time after this. The creation of new accounts and the re-verification of existing accounts has already been blocked on these older operating systems as well.

If you need to transfer your WhatsApp account to a new device, you can't transfer your chat history between platforms. However, you can export your chat history as an email attachment, so do this soon if you want to back up your old chats before the deadline.