This is a simultaneous release with Luna, but not in the Luna repositories.
The Paho client libraries have been in use for several years now by IBM and Mosquitto, amongst others, predating the Paho project itself. We consider them mature and suitable for production use, which is why we are proposing to graduate the project with this release.
The main functional addition is the support of the latest version of the MQTT 3.1.1 specification, an OASIS standard.