From the latest PTS patch notes:

• The Mac client will now require more RAM, with 8GB of RAM recommended.
• Machines with 4GB of RAM may see a negative effect on game performance.
• Only the 64-bit version for the Mac client will be supported moving forward.

(emphasis mine)

Given the amount of RAM the client can put to good use, this is a sensible decision. Not that Mac users need to worry, as OS X supports 64-bit GUI applications since Leopard, runs only on 64-bit capable CPUs since Lion, and has a 64-bit-only kernel since Mountain Lion url="https://en.wikipedia.org/wiki/OS_X#Versions"]1[/url.

Please also note that in order for OpenGL 4.1 to work, the minimum OS X version is Mavericks (10.9), and the Mac's graphics card must be capable to support it as well (or rather, its OS X driver). The minimum OS version requirement has been in place at least since 06/24/2015 (btw, this FAQ needs to be updated with the new recommended RAM specifications, @ZOS_MollyH ).

Edited to add this gem from the natch potes:

• We have upgraded the Mac client to use OpenGL 4.1.
• This will allow the Mac client to use higher resolution textures than previously.
• Improved facial animations will be included in a future incremental patch.

("future incremental patch" implies "to the PTS version during the current test phase", as there are multiple builds before the next live version is ready)

\o/