The engine is not fully open-source however — while most companies or groups upload their source codes with an open-source licence allowing developers to modify it freely, Crytek have avoided taking this route. Those willing to modify will have to purchase a commercial licence to access certain parts of the code, with legal restrictions of the code still fully applying.
“In the past, public Cryengine releases came with source code in a zip file included in the build,” wrote Davie Kaye, senior systems engineer at Crytek, in a blog post. “While this allowed users to customize systems as they saw fit, it was a simple drop of files. To see the difference in a set of files between one release and the next, both archives needed to be extracted and compared. Git makes this a lot easier, and since Git is decentralized, it can also be used just as effectively with no network connection.”
CRYENGINE. GIT. NOW!https://t.co/o03vLv1GoA
— CRYENGINE (@cryengine) May 24, 2016
You can see the entire source code for CryEngine on GitHub.