Drupal 8.5.0, the next planned minor release of Drupal 8, is scheduled for Wednesday, March 7, 2018. Minor releases include new features, usability improvements, and backwards-compatible API improvements. Here's what this means now for core patches.
The goal of the alpha phase is to begin the preparation of the minor release and provide a testing target for theme or module developers and site owners. Alpha releases include most of the new features, API additions, and disruptive changes that will be in the upcoming minor version.
In preparation for the minor release, Drupal 8.5.x will enter the alpha phase the week of January 17, 2018. Core developers should plan to complete changes that are only allowed in minor releases prior to the alpha release. (More information on alpha and beta releases.)
Developers and site owners can begin testing the alpha next week.
The 8.6.x branch of core has been created, and future feature and API additions will be targeted against that branch instead of 8.5.x. All outstanding issues filed against 8.5.x will be automatically migrated to 8.6.
All issues filed against 8.4.x will then be migrated to 8.5.x, and subsequent bug reports should be targeted against the 8.5.x branch.
During the alpha phase, core issues will be committed according to the following policy:
Most issues that are allowed for patch releases will be committed to 8.5.x and 8.6.x.
Drupal 8.4.x will receive only critical bugfixes in preparation for its final patch release window. (Drupal 8.3.x and older versions are not supported anymore and changes are not made to those branches.)
Most issues that are only allowed in minor releases will be committed to 8.6.x only. A few strategic issues may be backported to 8.5.x, but only at committer discretion after the issue is fixed in 8.6.x (so leave them set to 8.6.x unless you are a committer), and only up until the beta deadline.
Roughly two weeks after the alpha release, the first beta release will be created. All the restrictions of the alpha release apply to beta releases as well. The release of the first beta is a firm deadline for all feature and API additions. Even if an issue is pending in the Reviewed & Tested by the Community (RTBC) queue when the commit freeze for the beta begins, it will be committed to the next minor release only.
The release candidate phase will begin the week of February 21, and we will post further details at that time. See the summarized key dates in the release cycle, allowed changes during the Drupal 8 release cycle, and Drupal 8 backwards compatibility and internal API policy for more information.