This year NVIDIA has been following the "release early, release often" mantra with it seeming like two weeks can't even go by without seeing a new Linux driver -- whether it's a beta driver, an official driver update, or one of their legacy drivers picking up a few fixes (at times they have even released four drivers at once). On the opposite spectrum, AMD continues with monthly Catalyst driver updates on both Linux and windows. Rather than a continual stream of new public driver releases, AMD maintains a private beta program for their Catalyst Linux driver. This private program is made up of AMD developers, hardware vendors, users of different Linux distributions, other Linux vendors, and end-users. Phoronix has been a part of this program for years, but those testing this driver are under a strict Non-Disclosure Agreement with AMD regarding pre-releases of their Linux software. Today, however, AMD has decided to declassify some information pertaining to its Linux Graphics Driver Beta Program.
AMD's Linux Beta program allows the NDA-holding participants to have early access to the Linux graphics driver beta packages prior to their general availability. More on AMD's Linux release cycle and philosophy can be found in The Truth About ATI/AMD & Linux. This article is getting old, but it remains largely accurate with regards to their testing process, the release train, and release timing. A majority of what goes on with this private beta list relates to the distribution-specific packaging scripts and getting them ready for the next release. While the beta releases are closed to the general public, the packaging scripts are in fact freely available at anytime. These community-maintained scripts are housed over at Phorogit (a Phoronix Media property). This slide mentions there is "discussion on upcoming software", but frankly that's not too often the case. For example, the beta testers were not told in advance of AMD's decision to drop mainline R300-500 series support.
AMD's target participants for beta Linux driver testing is the general public, OEMs, ODMs, Linux vendors, ISVs, IHVs, open-source community members, enterprise and channel customers, and enthusiasts.