https://wccftech.com/apple-releases-ios-15-1-tvos-15-1-watchos-8-1-rc-for-developers/

Apple has just seeded the RC builds of iOS 15.1, iPadOS 15.1, tvOS 15.1 and watchOS 8.1 to registered developers.

Note: RC is available for those who have the previous beta installed on their compatible and registered devices.