Is Sentinel open source?

I'm curious about the development process of Sentinel. Can you tell me if Sentinel is open source? I understand that many cryptocurrency projects opt for open source development to encourage community contributions and transparency. If Sentinel is open source, could you provide me with more information on how to access the codebase and contribute to the project? Alternatively, if Sentinel is not open source, could you explain the reasons behind this decision and how the project ensures its security and reliability?