From Documentation

This table indicates the minimum supported version of ZK for use at specific servlet version.

Servlet compatibility table
Servlet version Java EE Jakarta EE
2.4 ZK 6 and later X
3.0 ZK 6 and later (*) X
4.0 ZK 6 and later (*) X
5.0 X ZK 9.6.0-Jakarta and later

(*) = Require configuration through web.xml or zk-web-fragment.jar See the ZK_Configuration_Reference/web.xml documentation page for more information on web.xml configuration.