Current devel version will be numbered 5.3.0 and it is planned to be released in the autum 2019.

Its features are documented here: https://www.kamailio.org/wiki/features/new-in-5.3.x

Previous devel, current stable, version was 5.3.x (released on October, 2019), see what was new in that release at:

• http://www.kamailio.org/wiki/features/new-in-5.3.x

This is a draft of new features added in devel version, manually updated, thus not always synchronized with what is new in source code repository.