Current devel version will be numbered 5.3.0 and it is planned to be released during 2019.
Previous devel, current stable, version was 5.2.x (released on November, 2018), see what was new in that release at:
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.
Embedded RTP and media processing functionalities for Kamailio
Filters to allow/block using whitelists/blacklist based on user agents, IP addresses, countries, domains and users. SQL injection attacks prevention. Blacklist of destinations where the called number is not allowed.
Added a new param in the cnxcc_set_max_credit() function to set the connect cost of a call.