docs/process/release_cycle.md

# Chrome Release Cycle

[TOC]

## Overview

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 four weeks before being shipped to stable. Once
a milestone reaches stable, weekly updates (called refreshes) are shipped to
stable to deploy security fixes and keep Chrome's
[patch gap](https://groups.google.com/a/chromium.org/g/security-dev/c/fbiuFbW07vI)
short.

## Extended Stable

Chrome Browser 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](#channel-lifecycle) to learn
more. The extended stable channel is only available to enterprises on the
Windows and Mac platforms, and can be enabled via enterprise policies. Biweekly
refreshes are shipped to extended stable.

While extended stable is only shipped to Windows and Mac, security fixes that
are relevant to any Chrome Browser platforms will be landed on the extended
stable branch for use by embedders. It's important to note that while the team
will make an effort to backport all important security fixes to extended
stable, complex and risky changes as well as larger features that improve
security (e.g.
[Site Isolation](https://www.chromium.org/Home/chromium-security/site-isolation))
may not be viable to backport and will only be available on the stable channel;
as such, using the stable channel and stable branches is recommended for any
team where security is a primary concern.

## Release Cycle
The diagram below shows when our different development checkpoints occur as a
milestone proceeds through our release cycle:

![Release Cycle](images/release_cycle.png)

* The primary development span (four weeks) of each milestone is not depicted
  above, though it is visible in the [channel lifecycle](#channel-lifecycle)
  below.
* You can find specific dates for each milestone's development checkpoints on
  our [release calendar](https://chromiumdash.appspot.com/schedule).
* Some dates will vary between different platforms; see the release calendar
  for specifics dates for each platform.
* Branch point dates are fixed, but release dates are
  subject to change based on a variety of factors (e.g. late-breaking
  regressions).
* Release dates are adjusted to avoid shipping new milestones to stable around
  major holidays to ensure proper coverage if issues arise. These adjustments
  are already depicted in our release schedule.

### Branch Point

The branch generated by the daily canary created at branch point is designated
as the milestone branch, which is then stabilized over the following four weeks.

Before Branch Point:

1.  All new features planned to launch in this milestone should be code complete
    (all primary functionality implemented). Features which are not code
    complete by branch point should be punted to the following milestone.
2.  All strings should be landed.
3.  All beta blocking bugs should be addressed.

Please consider [these guidelines](../release_branch_guidance.md) when landing
code around branch point.

### Beta Promotion

Shortly after branch, 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

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.

### Stable Promotion

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.

To get better statistical data for staged rollouts, each rollout will consist of
two separate builds which are identical, except for the build number. There is no
harm in being on the lower build number, and all users are expected to be
automatically updated to the higher build number as part of the rollout process.

### Stable Refresh

The stable channel is refreshed every week, and the extended stable channels is
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.

## Channel Lifecycle

The diagram below shows how different milestones proceed through Chrome's
different release channels:

![Channel Lifecycle](images/channel_diagram.png)

* As noted above, both stable and extended stable ship the same versions for
  the first four weeks of life, after which the two diverge.
* There is no extended beta channel; instead, the standard four week beta cycle
  is used to stabilize both stable and extended stable. Enterprises
  who choose to opt into the eight week extended stable should continue to run
  the beta channel as they do today in order to proactively identify issues
  that may impact their environments.

## Milestone Branch Support

The diagram below shows the lifespan of each milestone branch:

![Milestone Branch Support](images/branch_diagram.png)

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.