# Release Cadence

## Thunderbird Release Train Model

Thunderbird follows a release train model to ensure timely and predictable releases. This approach allows for regular feature rollouts, stability improvements, and bug fixes.

## General Release Cadence

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.

![](/files/mHJR9gqvhjXL1Tvjc3iw)

***

## **Release Channels**

### **Thunderbird Daily**

* **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.

### **Thunderbird Beta**

* **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.

### **Thunderbird Release**

* **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.

### **Thunderbird ESR (Extended Support Release)**

* **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.

***

## **Stabilization Milestones**

### **Daily Soft Code Freeze**

* A 1-week 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.

### **Pre-Merge Reviews**

* 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.

***

## **Sample Release Timeline for Thunderbird 136**

| Milestone                                | Date         |
| ---------------------------------------- | ------------ |
| Thunderbird 136.0a1 starts               | Jan 6        |
| Thunderbird 136.0a1 soft code freeze     | Jan 27–Feb 3 |
| Thunderbird 136.0a1 pre-merge review     | Jan 30       |
| 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       |

***

## **Thunderbird Milestones Calendar**

You can view Thunderbird release milestones on the [Thunderbird Release Calendar](https://calendar.google.com/calendar/u/0/embed?src=c_f7b7f2cea6f65593ef05afaf2abfcfb48f87e25794468cd4a19d16495d17b6d1@group.calendar.google.com).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://developer.thunderbird.net/releases/cadence.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.