GitHub Actions starts moving ubuntu-latest to Ubuntu 26.04 today

GitHub has started migrating the ubuntu-latest runner label in GitHub Actions from Ubuntu 24.04 to Ubuntu 26.04. The rollout runs gradually between 19 October and 19 November, so a workflow that used ubuntu-latest yesterday can find itself on a different image before the window closes, without any change to its own YAML.

Ubuntu 26.04 was already out of preview and fully supported on both x64 and arm64, now available directly as runs-on: ubuntu-26.04 or ubuntu-26.04-arm. GitHub’s own warning is blunt: the new image “includes updated, and in some cases removed, tools” compared to the old one, and that can break a build that pins to a specific preinstalled version. If you are not ready, pin the workflow to ubuntu-24.04 explicitly rather than relying on the label.

runs-on: ubuntu-24.04   # stay put until you've tested 26.04

Why it matters: this is a silent migration. Nothing in your repository changes, but the machine running your CI does, on a schedule you do not control precisely. Any workflow that assumes a specific compiler, interpreter or system library version from the default image is worth testing against Ubuntu 26.04 now, before the label moves it there for you.

The caveat: GitHub has not published exactly which tool versions move in this image, only that the full diff lives in the runner-images repository, so “test it yourself” is the actual guidance.