The next anticipated release after Isabelle2025-1 (December 2025) will be Isabelle2026 (October 2026). The hot phase of the release is presently scheduled for 14-Sep-2026..19-Oct-2026. The detailed plan is as follows:

• 17-Aug-2026: Isabelle2026-RC0 as informal preview
• 14-Sep-2026: Isabelle2026-RC1 as first formal release candidate
• 28-Sep-2026: fork of the isabelle-dev vs. isabelle-release repository
• 19-Oct-2026: final and unchangeable Isabelle2026 release

Important: Contributors need to have things ready for RC1, with a second chance until the repository fork. There need to be several weeks left to consolidate everything, before the release becomes final and unchangable (until the subsequent release).