Valve has relreased the 2013 build of the Source SDK. It includes support for OS X, Linux, Oculus Rift, and Steam Pipe.
It looks like Valve is changing the way mods are created from here on it. instead, you’ll have to use a Source game’s authoring tools instead of creating a mod through the SDK app, which will be removed from everyone’s tools library soon. Look’s like the Black Mesa devs may have some work to do. I hope Steam Pipe doesn’t break the mod.
Official Announcement: https://store.steampowered.com/news/10962/
Valve Time Article: https://www.valvetime.net/threads/source-sdk-2013-update-released.243620/
GitHub Page: https://github.com/ValveSoftware/source-sdk-2013
Valve Developer Wiki Page: https://developer.valvesoftware.com/wiki/SDK2013_GettingStarted