The open source software/gateware in OpenCPI is made available subject to the terms of GNU Lesser General Public License Version 3. This license was chosen to enable OpenCPI to be used by applications and other software under the more restrictive (and more open) GNU General Public License, as well as applications containing proprietary or otherwise restricted software. OpenCPI components can be developed based on proprietary source codes and still be used in OpenCPI applications, although this does not contribute to the community of users.
Thus while OpenCPI is completely open source, it can be used and embedded in closed applications, and make use of closed components.
You can find the LGPL3 license here.