Yarn v1 Classic unsupported - deprecation is due

[MikeMcC399]

Situation

• The action installs and runs projects based on Yarn v1 Classic yarn.lock lock files, alongside npm and pnpm projects as alternatives.

• GitHub Actions runner images such as ubuntu-26.04 continue to bundle Yarn 1.22.22.

• Yarn v1 Classic has however been in maintenance mode since Jan 2020 with no further support. Maintainers have indicated that they may formally deprecate Yarn v1 in Q3/2026.

Background

Yarn was originally released 14 years ago. The yarn@1.0.0 release followed then 8 years ago. With the release of Yarn 2 in Jan 2020, it was announced that Yarn v1 would enter maintenance mode and provide security fixes only. This is underlined by the notice on the source repo https://github.com/yarnpkg/yarn :

The 1.x line is frozen - features and bugfixes now happen on https://github.com/yarnpkg/berry

The last Yarn v1 Classic release was yarn@1.22.22 in March 2024.

Event	Date
Inital yarn@0.1.0 release	Mar 2012
yarn@1.0.0 release	Sep 2017
Yarn 2 GA	Jan 2020
yarn@1.22.22 release	Mar 2024
PGP signing key expiry	Jan 2030

Cloning the repo and attempting to run yarn test locally under Ubuntu 24.04.4 LTS produces failures on all Node.js versions from 8 - 26.

The PGP signing key 6A010C5166006599AA17F08146C2130DFD2497F5 expires on 2030-01-22T18:44:02Z.

Assessment

Yarn v1 Classic must be considered as no longer suitable for production usage.

• It is untested in currently supported Node.js versions >=20
• Emerging bugs and open issues are not addressed. PRs can no longer be submitted by community Contributors.

Recommendation

Deprecate Yarn v1 Classic usage in the Cypress action.

[MikeMcC399]

To support users moving from Yarn v1 Classic to Yarn Modern, PR #1823 is submitted to allow automatic installation of dependencies using Yarn Modern commands. Previously, only Yarn v1 Classic install commands were embedded in the action.

[MikeMcC399]

A sequence of deprecation could be:

1. documentation-only deprecation
2. runtime deprecation - producing a warning if Yarn v1 Classic is detected

Yarn maintainers may declare the official deprecation of Yarn v1 Classic, as they have indicated in yarnpkg/yarn#9062 (comment). This is supposed to be linked to the stable release of Yarn 6.x which is variously stated to be planned for Q3 2026 (or in other places "not before Q3 2026").

The deprecation proposed here is a longer term task, unless factors emerge which prevent legacy Yarn v1 Classic projects from being used in GitHub Actions. Deprecation provides users with advance notice to make plans for alternatives.

In the meantime, GitHub Actions continues to bundle Yarn v1 Classic in their runner images, for example in ubuntu-26.04.