Microsoft’s Azure Linux 4.0 Is Quietly Built on Fedora, GitHub Reveals

Microsoft has a Fedora-based Linux distribution on the way, and that is not a sentence many people expected to write. The upcoming Azure Linux 4.0 is built on Fedora, a detail Microsoft did not advertise but which its own GitHub repository quietly confirms.

The revelation came alongside a broader set of announcements at this week’s Open Source Summit, where Microsoft outlined updates spanning new Linux releases and agentic AI tooling.

Microsoft’s Push Into the “AI Native Era”

The news arrived during a keynote by Brendan Burns, co-founder of Kubernetes and Corporate VP for Azure OSS and Cloud Native at Microsoft. Burns framed the company’s direction as a shift away from cloud native toward what Microsoft is calling the “AI native era.”

The accompanying announcement covered a lot of ground. Here is a breakdown of the most important pieces.

The Linux Updates

On the Linux side, there were two key developments.

The first is Azure Linux 4.0, which is coming to Azure Virtual Machines as a public preview. It remains in active development, so there are no downloads available yet, though Microsoft has opened a sign-up form for early access.

The second is Azure Container Linux, which is now generally available, with a full rollout planned during Microsoft Build on June 2. This is an immutable, container-optimized operating system, meaning it ships with no package manager and a read-only system image by design.

That approach is aimed squarely at teams handling regulated or security-sensitive deployments. By keeping the system locked down, Microsoft can limit the attack surface while maintaining the supply chain end to end.

Building Blocks for Agentic AI

Microsoft also used the event to advance what it calls an open agentic stack, a set of tools for building AI agent systems.

Key components include:

• The Microsoft Agent Framework, an open source SDK and runtime for multi-agent systems. It consolidates earlier work from Semantic Kernel and AutoGen into a single foundation.
• The Agent Governance Toolkit, which handles identity, policy, and audit controls for AI agent deployments.
• Support for A2A, or agent-to-agent, protocols designed to enable communication across different vendors and frameworks.

Together, these pieces reflect Microsoft’s intent to position itself early in the emerging market for AI agent infrastructure.

The Fedora Connection Microsoft Didn’t Mention

Here is the most intriguing part. Microsoft’s announcement blog post does not mention Fedora even once. The Azure Linux 4.0 branch on the project’s GitHub, however, tells a very different story.

The README file for version 4.0 explicitly describes Fedora as an “upstream base” for Azure Linux. It characterizes the distribution as a collection of TOML configuration files and targeted overlays applied on top of Fedora. Packages, meanwhile, come directly from Fedora’s upstream repositories, with any deviations kept minimal and clearly documented.

This did not come entirely out of nowhere. Earlier reporting on a Fedora ELN SIG meeting revealed that Microsoft was backing a proposal to build x86-64-v3 packages for Fedora 45. Kyle Gospodnetich, a Linux engineer at Microsoft, was co-authoring that change proposal, with the motivation tied directly to Azure Linux’s need for the performance gains x86-64-v3 provides.

At the time, there was even talk of Microsoft forking the distribution outright, before the company was guided toward working within the Fedora ecosystem instead. That outcome looked uncertain back then. The 4.0 branch now confirms which path Microsoft chose.

Why Stay Quiet About It?

So why did Microsoft avoid mentioning Fedora in its announcement?

The likely reason comes down to industry relationships. Fedora effectively serves as Red Hat’s upstream, and Red Hat occupies an unusual position relative to Microsoft: it is both an Azure partner and a direct competitor in the enterprise Linux space. Highlighting a dependence on Red Hat’s upstream project would make for an awkward read in that context.

The Bottom Line

Azure Linux 4.0 represents a notable moment: Microsoft, once famously hostile to Linux, now building a distribution directly on Fedora and choosing to collaborate within its ecosystem rather than fork away from it. Paired with the general availability of Azure Container Linux and a growing stack of agentic AI tools, the announcements show how deeply open source is now woven into Microsoft’s strategy, even if the company was not eager to spell out every detail.