The Game Developers Conference 2015 Scheduler shows a session to be presented by Valve at next month's GDC on "The Future of High Performance Graphics," which will include members of the Frostbite engine team, Epic Games, Oxide Games, and Unity (thanks PC Gamer). With Valve focused on the ability to offer games independent of Windows, getting better control over the graphics API seems a next logical step following the launch of SteamOS, and the description of the session suggests that's what this is about:

Join us for the unveiling of Khronos' glNext initiative, the upcoming cross-platform graphics API designed for modern programming techniques and processors. glNext will be the singular choice for developers who demand peak performance in their applications. We will present a technical breakdown of the API, advanced techniques and live demos of real-world applications running on glNext drivers and hardware.