Programming OpenGL on macOS
AGL/Carbon
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/NSGL
Cocoa is the modern API with Objective-C bindings. Mac OS X 10.5 Leopard ships 64 bit versions of Cocoa.