LiveKit Cloud runs the same open-source servers that you can find on Github. It provides the same APIs and supports the same client SDKs. An open source user can migrate to Cloud, and a Cloud customer can switch to self-hosted at any moment. As far as your code is concerned, the only difference is the URL that it connects to.
LiveKit Cloud is a fully-managed, cloud-hosted, global network of LiveKit servers. Using LiveKit Cloud allows you to focus on building your application, without worrying about deploying and maintaining servers yourself.