The next anticipated release is Isabelle2021-1 (December 2021): as the distance between two releases is usually 8–10 months, there are sometimes 2 releases per year. This explains the slightly odd name tag, but in all other respects, Isabelle-2021-1 should be a perfectly normal official release.
The next anticipated release is Isabelle2021 (February 2021). The hot phase with release candidates will presumably be 28-Dec-2020 .. 15-Feb-2020.
The official Isabelle2020 release is scheduled for April 2020. This blog entry is dynamically updated to follow the sequence of public release candidates.
Notifications about the Isabelle release process.