Cobalt Versioning

  • Cobalt versioning follows the format: [Major Version].[Purpose].[Minor Version].[Build ID], representing the yearly set, build purpose, update revision, and a unique build identifier.

  • Stable LTS releases, recommended for YouTube Certification and device updates, have Minor Versions that are multiples of 10 (e.g., 24.lts.10, 24.lts.20).

  • The Build ID is a monotonically increasing number reflecting the state of the source code and is incremented with each commit.

  • Pre-built Evergreen binaries are currently only provided for Stable LTS releases and can be found on the Cobalt release page.

  • For certification, only use Stable Cobalt versions with Minor Versions in multiples of 10, aligning with previous certification policies.

Cobalt versions, as they appear in the user agent, use semantic versioning and have the following structure:

[Major Version].[Purpose].[Minor Version].[Build ID]

The definitions of these version structure components are described below.

Example Cobalt versions would be:

  • 24.lts.1.1032413
  • 24.lts.2.1032464
  • 24.lts.3.1032501
  • 24.lts.10.1032622
  • 24.lts.12.1032692
  • 24.lts.20.1032766
  • ...
  • 24.lts.40.1032940

Major Version

Cobalt major version is tied to a yearly release cycle and this number indicates the yearly set that this version of Cobalt supports. It is the last two digits of the year of the target yearly set. For example for the 2024 yearly set, this value will be 24.

Purpose

The purpose of this build, usually named after the reason that a branch is cut. On the master branch it will be master, and on LTS branches for example it will be lts.

Minor Version

The current update revision number (e.g. release number). This will always be 0 on the master branch. When a release branch is cut, will be modified to start at 1, and be incremented each time a release or update is released. It is possible that multiple updates are released off of the same release branch, if new bugs are discovered and fixed.

Build ID

The Cobalt Build ID represents fine-grained information about the state of the source tree for a given build. The number is simply a sequential, monotonically increasing commit number. E.g. every cherry-picked or merged commit on the release branch increments it by one.

A src/cobalt/build/get_build_id.py script is used during the build to resolve the build ID number during builds, and can be similarly used to verify it in a checkout. Here is an example to get the Build ID in 24.lts.40 tag: ```sh $ git checkout 24.lts.40 HEAD is now at ecdcfdb8e5a Cherry pick PR #3084: Add idl definition for PersistentSettingLogtraceEnable getter and setter (#3091) $ cobalt/build/get_build_id.py 1032940

An example to remove two commits

$ git reset --hard HEAD^^ HEAD is now at 0fab5f48a97 Cherry pick PR #2930: Add blackbox test for logTrace and watchdog violations APIs. (#3059)

The Build ID is decreased by two

$ cobalt/build/get_build_id.py 1032938 ```

Stable Version

Starting with Cobalt 24, the version numbering scheme for LTS Major and Minor Stable releases are now numbered by multiples of 10. This change aligns with semantic versioning, adds more sensible differentiation for Stable vs incremental non-Stable releases, and enables the Cobalt team to deliver faster fixes, optimizations, and features to our mutual users. Please only use Cobalt LTS releases with Minor Version that are multiples of 10 for YouTube Certification and Cobalt Device Maintenance Updates.

NOTE: Pre-built Evergreen binaries are only available for Stable (non-RC) releases at this time and available on the release page: * https://github.com/youtube/cobalt/releases

For Example:

Cobalt Release Stable (Usable for cert)?
24.lts.1 No
24.lts.2 No
24.lts.3 No
24.lts.10 Yes
24.lts.11 No
24.lts.12 No
24.lts.20 Yes

FAQs

What version should I use for certification?

  • Only Stable Cobalt versions. This is the same policy as before with the Cobalt 24 numbering scheme as the only change.
  • E.g. Cobalt 24.lts.10, 24.lts.20, ..., 24.lts.40

What about Evergreen binary versions?

  • Stable Evergreen binaries will also be numbered similarly with minor version numbers
  • E.g. 24.lts.40 (Evergreen binary version 4.10.2)

Will Evergreen binaries be provided for all Cobalt releases?

  • No, at this time, pre-built Evergreen binaries will only be available for Stable releases (e.g. 24.lts.10, 24.lts.20, …, 24.lts.40). In the future, the Cobalt Team is planning to release matching pre-built Evergreen binaries for RC (non-Stable) releases that will be announced at a later time.
  • Please refer the release page to get all the available binaries:
    • https://github.com/youtube/cobalt/releases

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