Confusing the Big Sur beta process somewhat, Apple has released macOS 11.0.1 beta 1 to developers prior to the release of Big Sur to the general public.
New betas are able to be downloaded from the Apple Developer Center by anyone enrolled in the Developer Beta program. Devices with the proper configuration profile installed can also update to the newest build as an over-the-air update.
This release follows after ten betas of 11.0, which Apple released to developers on October 14. It now significantly lags behind Apple's other operating systems, including iOS 14, iPadOS 14, watchOS 7, and tvOS 14, which have all seen release to the public.
Though Apple hasn't explained why macOS Big Sur is slow to release, it is likely due to it being a major update that has to be functional both for existing Intel-based Mac systems as well as future models running on Apple Silicon, chips of Apple's own design. Apple has previously declared it would bring out its first Apple Silicon Mac before the end of 2020, which would require macOS Big Sur to function.
It is unclear why this beta is releasing today, other than a possible leak prevention measure. It could indicate that macOS 11.0 is releasing to the public soon, but more likely it shows that macOS 11.0.1 will be shipping on whatever Macs are announced in November.
AppleInsider, and Apple itself, strongly suggest users avoid installing betas on to "mission-critical" or primary devices, due to the potential for data loss or other issues. It is instead recommended to install betas onto secondary or non-essential devices, and to ensure there are sufficient backups of important data beforehand.
Update: Apple on Thursday issued a public beta version of Big Sur 11.0.1 for testing.