The stable, default branch is now in line with unstable. This will break your saves.
The previous stable is available as legacy_august_2020 in the beta builds if you want to keep an existing save.
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 5454592 · legacy_august_2020 branch
Steam updated · First observed