MacRumors published a story that Apple has released the second beta of tvOS 18 to registered developers.
Apple Seeds Second Beta of tvOS 18 to Developers
Apple today seeded the second beta of the upcoming tvOS 18 refresh to developers for testing purposes, with the beta coming two weeks after the first beta came out following the WWDC 2024 keynote event.
Registered developers are able to download the tvOS 18 update by opting in to the beta through the Settings app on the Apple TV. A registered developer account is required.