1.4 is the current development release.
Migrating to Wicket 1.4
Getting and building it
http://wicket.apache.org/building-from-svn.html describes how to get and build Wicket 1.4.x.
Snapshots can be found in this maven repository and has version 1.4-SNAPSHOT:
http://wicketstuff.org/maven/repository
JDK 1.5
Minimum Java version is now 1.5.
Spring Support
Spring Modules
wicket-spring and wicket-spring-annot modules have been merged. If your project depends on wicket-spring-annot simply replace it with a dependency on wicket-spring.
If you are using the SpringBean annotation, you need to add wicket-ioc, starting from version 1.4-m2.
SpringWebApplication
SpringWebApplication has been deprecated in favor of SpringBean annotation. See SpringWebApplication javadoc for how to setup SpringBean based injection.
Validators
NumberValidator has been deprecated and broken into three more generic validators: RangeValidator, MinimumValidator, MaximumValidator. Likewise, the corresponding resource keys have also been changed (eg NumberValidator.maximum resource key has become MaximumValidator). NumberValidator.POSITIVE and NEGATIVE have been deprecated without a replacement, they were too confusing to the users with regard to whether or not they included zero - the same result can be easily reproduced by either Minimum or MaximumValidator.