It will be fully released to everyone in the 12.5 Major release.
The benefit of using PBR materials is the potential for much higher quality renderings but also that the export of materials to other software will work much better.
PBR features will be released as a "silent release" currently, meaning that it will not be visible to anyone unless they first enable it in the release debug dialog (Ctrl+Alt+F12).
The idea with this "silent release" is to make it possible for Extension developers to create PBR material content for the upcoming CET 12.5 release which will enable PBR material functionality to all users!
If enabled in this dialog, Material Lab will have 2 modes and the classic mode will have a new button called "convert to PBR". PBR materials will be saved in *.gm files, but PBR materials saved in GMaterial file will not be possible to open in a version of CET prior to 12.0 minor.
A PBR material differs from a classic material in that all channels support textures. Also, the channels are more and different in PBR compared to classic materials. CET uses the Disney principled Metallic/Roughness PBR model.
Classic materials can be converted into PBR materials by a simple click on the "convert to PBR" button in Material Lab. The material can then be saved and it will be a PBR material!
You can also convert many classic materials into PBR materials at once using the batch converter tool.
Note that just converting a material into PBR doesn't magically make it much better than before. To actually utilize the PBR technology to its full extent you need to add information. In this case more textures in several channels.
What channels and how those are supposed to look are beyond the scope of this article and it is also different depending on what type of material you are creating. There are several online libraries of PBR materials that you can use as inspiration on how to create your own. There are also commercial scanners available that will output the required textures from a given physical sample of the material.
Support for 3rd Party Materials
The PBR technology used in CET works with most commercial material libraries. Material Lab has support for drag and drop of a zip file containing multiple textures that make up one single PBR material. Material Lab will try to load each texture into the appropriate channel using the names of the files within the zip file (for instance a file name containing "albedo", "base" or "diffuse" will load into the base texture channel).
You can also drag and drop a single texture into the appropriate texture channel and Material Lab will look in the corresponding folder for other texture files and give the user a question if they want to load them into the appropriate texture channels.