Release Cadence
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Thunderbird follows a release train model to ensure timely and predictable releases. This approach allows for regular feature rollouts, stability improvements, and bug fixes.
The general release cadence consists of 4-week cycles, with each branch corresponding to a specific release channel. Each branch, starting from comm-central, is based on the previous branch.
Release Timeline: A new major version of Thunderbird Daily begins every 4 weeks.
Releases: Thunderbird Daily is automatically released on a daily basis from comm-central.
Release Timeline:
A new major version of Thunderbird Beta begins every 4 weeks.
4 weeks after Daily starts for a new version, comm-central is merged into comm-beta.
Releases: Thunderbird Beta for this version is released weekly for the next 3 weeks.
Beta 1: Includes the merged code.
Beta 2 and above: Include any new uplifts.
Release Timeline:
A new major version of Thunderbird Release begins every 4 weeks.
3 weeks after Beta starts for a new version, comm-beta is merged into comm-release.
1 week after this merge, the monthly Thunderbird Release is published.
Releases: Thunderbird Release is released every 4 weeks, with point releases as needed every 2 weeks.
Release Timeline: The code from comm-release is merged into comm-esr<version> once a year.
Releases: Thunderbird ESR is released every year, typically in July, with point releases as needed every 2 weeks.
A 4-day soft code freeze occurs for comm-central prior to merging into comm-beta.
During this time:
Risky code should not land in comm-central.
Features controlled by a feature flag that were disabled in Daily should not be enabled.
Prior to both merges, reviews are conducted for all changes included in the merge.
Code may be backed out if:
It is deemed too risky.
It introduces new crashes or high-severity bugs.
It reduces the overall quality of Thunderbird.
It introduces a bug and a follow-up fix cannot be provided in a reasonable timeframe.
Thunderbird 136.0a1 starts
Jan 6
Thunderbird 136.0a1 pre-merge review
Jan 30
Thunderbird 136.0a1 soft code freeze
Jan 30–Feb 3
Thunderbird merge 136.0a1 central → beta
Feb 3
Thunderbird 136.0b1
Feb 5
Thunderbird 136.0b2
Feb 12
Thunderbird 136.0b3
Feb 19
Thunderbird 136.0b4
Feb 24
Thunderbird 136.0b4 pre-merge review
Feb 24
Thunderbird merge 136.0b4 beta → release
Feb 25
Thunderbird 136.0
Mar 4
Thunderbird 136.0.1
Mar 18
You can view Thunderbird release milestones on the Thunderbird Release Calendar.
