Yes, it absolutely does! The chat UX, add-ons (deep research, code interpreter, RAG, etc.), and SSO are MIT licensed. Most deployments of Onyx are using the pure FOSS version of Onyx. Many individuals / teams have done extensive white labeling (something that OpenWebUI doesn't allow).

We have https://github.com/onyx-dot-app/onyx-foss, for a fully MIT licensed version of the repo if you want to be safe about the license/feel freedom to modify every file.