Hello! I noticed the LSP was not working when you ran the Theia-vscode side of things. To solve this I downgraded the vscode-extension-self-contained/package.json "vscode-languageclient": "^8.0.1" to "vscode-languageclient": "6.1.4" Then had to update the extension.ts imports to: import { LanguageClient, LanguageClientOptions, ServerOptions } from '**vscode-languageclient**'; Figured I'd post this here to let you know!