Deep Silver and 4A Games have released a dedicated Mac version of Metro: Last Light which can be downloaded today via Steam. It'll be downloadable via the App Store as well, but is not yet available there. Additionally, a Linux version is also in development and scheduled for release later this year.
Metro: Last Light on Steam will reportedly support Steam Play, meaning owners of any Steam version will automatically find the game added to their PC, Mac, and Linux Steam libraries.
Both Mac and Linux versions will receive the same DLC packages as the PC and console versions. The game's Season Pass, alongw ith the already released Faction Pack and Tower Pack will be available at launch for the Mac Steam release. The upcoming Developer and Chronicles Packs will be released on Mac alongside the PC and console releases.