MySQL 8.1 Release Notes
MySQL 8.1.0 Source Code Documentation
MySQL 8.1 supports upgrades from previous versions of MySQL as specified here:
Upgrades from MySQL 8.0 to 8.1 are supported between General Availability (GA) releases only. For MySQL 8.1, it is required that you upgrade from a MySQL 8.0 GA release (8.0.11 or higher). Upgrades from non-GA releases of MySQL 8.0 are not supported.
Upgrading to the latest release in the series is recommended before upgrading to the next release series. For example, upgrade to the latest MySQL 8.0 release before upgrading to MySQL 8.1.
Upgrades that skip release series are not supported. For example, upgrading directly from MySQL 5.7 to 8.1 is not supported.