Apple has seeded the release candidates of macOS Sequoia 15.1, iOS 18.1, iPadOS 18.1, tvOS 18.1, and visionOS 2.1 to developers.
A release candidate (RC), also known as gamma testing or “going silver”, is a beta version with the potential to be a stable product, which is ready to release unless significant bugs emerge.
Registered developers can download the betas via Apple’s developer portal. Or they can be downloaded over-the-air once the proper configuration profile has been installed from the Developer Center.