[gigel82]

"Hidden APIs" is clickbait; VS Code is open source. Unless they're saying the published VS Code binaries are somehow altered to offer the APIs that are not otherwise available in the open source repository (which is not the case).

[tristan957]

VSCode is not open source. Code-OSS is open source and is what is published at https://github.com/microsoft/vscode. VSCode is a proprietary application you download from Microsoft that is a distribution of Code-OSS with Microsoft branding and presumably some proprietary changes.