[Policy] Define explicit Drupal 10 end of life date of the December 2026 minor release window regardless of Drupal 12 release date

Problem/Motivation

Currently, depending on the release of Drupal 12, Drupal 10 may be end of life mid-June, early August or early December in 2026. See #3449806: [12.x] [meta] Release Drupal 12 in 2026 which currently says "Drupal 12 will be released in mid-June, early August, or early December 2026" and https://www.drupal.org/about/core/policies/core-release-cycles/schedule which currently says "Drupal 10 will reach end of life mid-late 2026, when Drupal 12 is released. The exact date is not yet set.".

We have announced this at https://www.drupal.org/blog/drupal-10-will-be-supported-until-the-releas...

The core team would like to get to a stable Drupal 12 by mid-June, but the three windows give an uncertainly to the Drupal 10 EOL timeline. However with a theoretic last Drupal 12 release window in early December 2026, there would nonetheless be a possibility that Drupal 10 would be supported until early December 2026 under the current communicated process.

Steps to reproduce

Proposed resolution

1. Drupal 10 end of life
   current text

   Drupal 10 will reach end of life mid-late 2026, when Drupal 12 is released. The exact date is not yet set. Check out the sample release schedule for estimates.

   proposed text

   Drupal 10 will reach end of life on December 9, 2026, after Drupal 12 has been released. No new releases of Drupal 10 will be made after this date.

   Note: The exact date of December 9 is pending final confirmation with the release managers, Drupal Association, etc. depending on 2026 event schedules etc.

2. In the June or August scenario, the 12.1 release announcement will include a section at the bottom mentioning that D10 is EOL. In the December scenario, the 12.0 announcement will include a section at the bottom mentioning that D10 is EOL.

3. The Security Team will issue at least one PSA announcing the D10 EOL.

4. Regarding the December 2026 core security window on December 16, 2026: No security advisories affecting Drupal 10 will be released on this date, and the window will most likely be canceled entirely. This will be mentioned in the release announcement and/or PSA about the D10 EOL.

Remaining tasks

Signoffs needed to make this change would be:

1. ✅ RTBC here
2. ✅ Discuss with the Security Team.
3. Release managers, since they are most directly affected in the RASCI. If we have that consensus, then:
4. Full core leadership team through our decision-making process, as this creates additional work for all committers in committing to three major branches and their assorted minors if a June release of 12.0.0 is achieved.
5. Potential followup issue: Plan for how to support contrib in the June scenario where they feel they have to support three majors for six months

When fully agreed, update the release schedule page and add a change record.

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet