The Sims 4 on Mac is scheduled for release on the 17th February 2015. The Get To Work! expansion pack will then be released in April; at the same time as the PC edition.
If you’ve already bought The Sims 4 on PC, you will be able to download it for free on Mac. Future customers get the same deal. It’s also been mentioned that save files will be compatible between the different editions, although there’s no word as to whether the game will automatically keep households synced.