The head of master will generally have New Relic's latest release. However, New Relic reserves the ability to push an edge to the master. If you download a release from GitHub, use the appropriate tag. New Relic usually pushes beta versions of a release to a working branch before tagging them for General Availability.
Fork away and feel free to send us pull requests (branches only please) for any ideas or bugfixes you come up with at support.newrelic.com.