GitHub Apps making server-to-server requests use the installation's minimum rate limit of 5,000 requests per hour. Organization installations with more than 20 users receive another 50 requests per hour for each user. Installations that have more than 20 repositories receive another 50 requests per hour for each repository. The maximum rate limit for an installation is 12,500 requests per hour.
GitHub Apps can also act on behalf of a user, making user-to-server requests.
User-to-server requests are rate limited at 5,000 requests per hour and per authenticated user. All OAuth applications authorized by that user, personal access tokens owned by that user, and requests authenticated with that user's username and password share the same quota of 5,000 requests per hour for that user.