Wargaming officially confirmed the HD/SD client split. During the installation, you will be able to select whether you want a HD client with HD textures or a SD client with lower resolution textures. Only 64bit OS users will be able to install the HD version.
You will also be able to either "upgrade" your client to HD from SD (by downloading additional textures) or "downgrade" your HD client to SD (by having the game delete the HD textures you no longer need).
A bunch of replies to commonly asked questions:
- Mods should work with both versions the same (WG however does not as usual guarantee their functionality);
- You will not have to choose the version of client every patch, the system will automatically download the SD/HD patch based on your settings;
- The SD client is roughly 6GB smaller than the HD one (unpacked installation), you will download roughly 3GB less if selecting the SD client;
- The HD client is currently called "beta HD client" because WG is constantly adding new HD content and its size (composition) is not final.