Deemwar Monads & Abstractions

ubuntu-latest moves to 26.04

Source: [Ubuntu] `ubuntu-latest` label will use Ubuntu 26.04 in November 2026, by GitHub (actions/runner-images)

GitHub moves the x64 ubuntu-latest label from Ubuntu 24.04 to Ubuntu 26.04. The rollout is gradual; the notice does not say how jobs are assigned during it. The 26.04 image readme lists Java 25 as the default JDK.

Oct 19 rollout starts

Nov 19 planned finish

17 → 25 default Java

What changes and when

The notice says the change rolls out over several weeks from October 19, 2026, and GitHub plans to complete it by November 19, 2026. The notice doesn't say how jobs are assigned during the rollout; plan for either image until November 19.

Before Oct 1924.04

Oct 19rollout starts

Rolloutplan for either image

Nov 1926.04, planned

The notice and the readme disagree

As of October 18, 2026, the notice table says Java 17.0.20+1 stays the default on 26.04: “Default version remains Java 17”. The Ubuntu 26.04 image readme marks 25.0.4+1 as the default instead. Commenters on the issue have raised the mismatch since September 24, and Alex Remniov posted about it on X. GitHub may update the notice; the readme describes the image itself.

Two more differences: the 24.04 readme lists Java 8 (8.0.504+1) and the 26.04 readme does not. The notice table lists Docker Buildx 0.37.0 for both images, while both readmes list 0.38.0.

Versions, from the two readmes

Tool	Ubuntu 24.04	Ubuntu 26.04
Java default	17.0.20+1	25.0.4+1
Java 8	8.0.504+1	not listed
Docker Client	28.0.4	29.4.2
Docker Compose	2.38.2	5.1.3
Docker Buildx	0.38.0	0.38.0

What to do

Pin the imageSet runs-on: ubuntu-24.04 on jobs that must not change.

Pin the JDKSet the Java version explicitly with actions/setup-java instead of relying on the image default.

Test earlyRun the pipeline once on the ubuntu-26.04 label before the rollout reaches it.

Diff the readmesCompare the 24.04 and 26.04 readmes for every tool the build uses.

Guardrails

Trust the image readme over the summary table.
Treat a red build in this window as a possible image change.
Java 8 builds need their own JDK setup on 26.04.
Check Compose 5 against existing compose files.

Links

The notice: actions/runner-images issue 14748.

Ubuntu 26.04 image readme · Ubuntu 24.04 image readme.

The X post by Alex Remniov on the Java mismatch.

A link to the Short on this topic will be added here.

Sources: dates and the Java 17 line from issue 14748; all versions from the two image readmes, read October 18, 2026.

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