Which macOS version was the first to include the Metal graphics API?

The first macOS version to include the Metal graphics API was OS X El Capitan. Apple brought Metal to the Mac in OS X 10.11, after first introducing the technology for iOS 8 in 2014.

Metal is a low-overhead graphics and compute framework that gives applications more direct control over a device's graphics processor. By reducing the work performed by traditional abstraction layers, it can improve rendering efficiency for games, professional visual applications, and system effects. Apple said El Capitan's implementation could accelerate system-level graphics tasks as well as demanding applications.

The main historical distinction is between Metal's debut on Apple's platforms and its debut on the Mac. Metal first appeared on iOS devices using Apple's A7 chip or later, but it did not arrive in OS X until El Capitan, released in September 2015. Mac support also depended on hardware: Apple listed compatible Macs generally dating from 2012 onward, so installing El Capitan alone did not guarantee Metal support.