If you purchased a MacBook Pro Retina 15″ model this year after late May, you may have purchased the model with the AMD Radeon R9 M370X discrete graphics processor. I wish AMD and Apple would update their official drivers more frequently, but at least we still have an option to update unofficially on our own. I have just used the process in this article to update to version 16.9.2 of the Radeon drivers to verify it still works correctly.
Update 2: As of October 2016, AMD and Apple have yet to release an updated Radeon driver since April. I’ve not yet tested them, so proceed at your own risk. Additionally, if you read the comments there are now a couple of sites that claim they have pre-packaged modified drivers available. However, the steps described below should still work if you want to make sure you have the latest and greatest unsupported driver from AMD for your Radeon R9-based Mac. I recommend you use this supported driver at this time. This updated driver fully supports Rainbow Six Siege and other new games. Update: As of April 2016, AMD has finally released an updated Radeon Boot Camp driver for the 2015 MacBook Pro Retina 15″ and similar iMac Retina models.