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Kairos release v4.0.0

· 3 min read
Mauro Morales
Mauro Morales

Kairos v4.0.0 is the result of a clear architecture path we have been building over time: first standardizing image creation with kairos-init, then making that flow easy to run anywhere with Kairos Factory and kairos-factory-action, and finally introducing Hadron.

In March 2025, we introduced kairos-init, a foundational shift that removed Dockerfile-heavy distro logic and standardized how we transform OCI bases into Kairos images.

From there, we focused on operationalizing that model so anyone could run it. With Kairos Factory, users can build and maintain their own Kairos pipelines using the same tooling we run in production.

In December 2025, we introduced Hadron, our upstream-first Linux base for immutable systems. In v4, Hadron artifacts are what the project publishes in its release flow.

At the same time, distro flexibility remains core to Kairos. This is visible in active community work such as Oracle Linux support in kairos-io/kairos#3987.

For additional migration and build context, read Hadron-Only Artifacts with Ongoing Distro Support.

What v4 delivers in practice​

The key technical reassurance in v4 is compatibility in the build pipeline. Between v3.7.2 and v4.0.0, the kairos-init version did not change.

This matters because kairos-init is where the core Kairos transformation components are pinned. When that set of components is unchanged, build behavior remains compatible in practice across releases. In practical terms, if your non-Hadron flavor pipeline built successfully with v3.7.2, it should continue to build with v4.0.0 under the same assumptions.

For the complete technical details of v4.0.0, see the release notes: kairos v4.0.0.

How to switch to v4​

There are two official paths to adopt Kairos v4, and the right one depends on your environment and goals.

One path is to use Hadron-based images, which are now published as part of the project release flow.

The other path is to keep your current distro flavor and build your own v4 release pipeline. With Kairos Factory, you can build and publish your flavor using the same production tooling model we use ourselves.

For migration guidance and build details, read: Hadron-Only Artifacts with Ongoing Distro Support.