State of AMD drivers in 16.04 [closed]

I am really confused about the state of AMD drivers on 16.04

My question is six-fold.

1. What is the difference between
   • The amdgpu driver,
   • The radeon driver, and
   • The amdgpu-pro driver?

2. When would each of those drivers be used?

3. Are they all open-source?

4. Can you switch between them?

5. Which GPUs are supported?

6. Is AMD working on an fglrx replacement for 16.04?

As I do not have an AMD card, I am unable to experiment.

I understand this is a broad question, but I want this to be a canonical question :)

Here's what I've been able to find so far:

1. • A: The amdgpu driver, pre-installed in 16.04, is used for AMD's newest graphics cards. ³

   • B: The radeon driver, also pre-installed in 16.04¹, is a replacement for the fglrx driver¹, and is used for older AMD cards that amdgpu doesn't support.

   • C: amdgpu-pro is not its own driver, but rather an overlay on top of amdgpu². It is optimized for gaming².

2. I think Ubuntu decides automatically. Although the amdgpu-pro driver has to be downloaded manually.

3. • The amdgpu driver is completely open-source
   • The radeon driver is completely open-source
   • The amdgpu-pro driver is partially open-source

4. I have no idea. Probably not.

5. Still have to do more research....

6. amdgpu-pro is the replacement for fglrx.