Git Updater is able to access the GitHub API by default. This means that any plugins or themes that are hosted on GitHub and have the correct header will be seen by Git Updater and the GitHub API will be polled for update checks.
These update checks occur every 12 hours and the data is cached. The cache can be refreshed by using the Refresh Cache button in the Settings.
Additional API plugins for GitHub Gist, Bitbucket, GitLab, and Gitea are available via a one-click install and activate from the Add-Ons tab in the Git Updater Settings.