Programming OpenGL on macOS
AGL is the old Carbon-based API with C bindings. The Carbon part needed for windowing and event handling are not thread-safe. There is no 64 bit version of this API.
Cocoa is the modern API with Objective-C bindings. Mac OS X 10.5 Leopard and later ships 64 bit versions of Cocoa. Using OpenGL in Cocoa requires you to include the frameworks "Cocoa" and "OpenGL" in your project.
For a long time, MacOS X supported OpenGL only in version 3.2 and below. MacOS X 10.9, "Mavericks", added support for OpenGL 3.3, 4.0 and 4.1.