Chrome is planning to migrate from its current six week release cycle to a new four week release cycle in Q3 2021, tentatively targeting M94 as the transition point. The content below (which describes the new four week cycle) is not yet applicable and is subject to change over the course of the next few months.
Chrome ships a new milestone (major version) to the stable channel every four weeks. The new milestone is developed on main for four weeks (beginning on branch point for the previous milestone) before the milestone's branch is cut, which is then stabilized for six weeks before being shipped to stable.
Chrome also maintains every other milestone branch for four additional weeks by backporting important security fixes to create an extended stable channel, where a new milestone is shipped every eight weeks. During the first four weeks of this milestone, both stable and extended stable are shipped identical releases; see the channel lifecycle to learn more. The extended stable channel is only available to enterprises, who can enable it via enterprise policies.
Biweekly updates (called refreshes) are shipped to both the stable and extended stable channels to deploy security fixes (alongside selected, low-risk regression fixes) and keep Chrome's patch gap short.
The diagram below shows when our different development checkpoints occur as a milestone proceeds through our release cycle:
All new features planned to launch in this milestone should be code complete (all primary functionality implemented) by feature freeze. Features which are not code complete by feature freeze should be punted to the following milestone.
The branch generated by the daily canary created at branch point is designated as the milestone branch, which is then stabilized over the following six weeks. All strings should be landed by branch point, and all beta blocking bugs should be addressed as well.
Please consider these guidelines when landing code around branch point.
After two weeks of stabilization, the new milestone is shipped to the beta channel for the first time. A new build is shipped to beta each following week for three additional weeks so that the release spends four weeks total in the beta channel.
Stable cut is the day that our stable release candidate build will be generated. This build is then shipped to beta to gather user feedback for one week. Any changes that land after stable cut may or may not be included in the stable release, and thus all stable blocking issues must be fixed by stable cut.
After four weeks in the beta channel, the new milestone is shipped to the stable channel for the first time. The rollout is staged over time so that any early issues that arise can be addressed before they reach all users. The new release generally reaches all users within one to two weeks unless major issues arise that cannot be addressed quickly.
The stable and extended stable channels are refreshed every two weeks. These refreshes typically contain important security fixes as well as any urgent regression fixes that may be available at the discretion of the release team.
The diagram below shows how different milestones proceed through Chrome's different release channels:
The diagram below shows the lifespan of each milestone branch:
While a milestone branch is active, branch infrastructure (e.g. branch CQ) will be kept active, and important security fixes will be considered for backport. An endpoint which describes currently active branches and their respective channels is under consideration, and if built will be available ahead of launch of the new extended stable channel and the four week release cycle.