Microsoft handed the developer world another free gift on May 18, announcing at Open Source Summit North America the public preview of Azure Linux 4.0 and the general availability of Azure Container Linux. It is the company’s first general-purpose server Linux, it is open source, and it costs nothing to download. The catch is the one Microsoft rarely puts on a slide: more than two-thirds of customer compute cores on Azure already run Linux, and every new free Linux release makes that paid cloud stickier, not less essential.
That tension runs through the whole redemption story. Microsoft has gone from calling Linux a disease to maintaining its own distribution, and the contributions are real. So is the business logic that shaped every one of them.
Azure Linux 4.0 Arrives Free, and Tied to Azure
The new release is a Fedora-derived, RPM-based distribution that Microsoft builds and maintains itself. It ships with a smaller default package set than its predecessor, a tighter default-deny security policy, and kernel support for the latest ARM and AMD instances Azure rents out. Microsoft is positioning it as a hardened base for cloud-native and AI workloads. You can read the full slate in Microsoft’s Open Source Summit announcements.
None of that is fake openness. The code is public, the license is permissive, and any engineer can pull it. But the distribution is tuned for one place above all others, and that place bills by the hour. Azure Container Linux, the companion release, is built on Flatcar, an open project Microsoft acquired rather than wrote from scratch.
So the question worth asking when a trillion-dollar company gives software away is the simple one: what does the gift make you need next? With Azure Linux, the answer is the cloud it was optimized for.
From ‘Cancer’ to a Platinum Seat at the Table
To see how far this has traveled, you have to remember how hostile the starting point was. Steve Ballmer, Microsoft’s chief executive at the time, called Linux “a cancer” in 2001. The company also funneled money into the SCO Group’s copyright fight against Linux, claimed the system infringed 235 unnamed Microsoft patents, and pressed Android hardware makers into royalty deals. The posture predates even that, tracing back to co-founder Bill Gates’ 1976 “Open Letter to Hobbyists,” which scolded enthusiasts for copying software without paying.
Then Satya Nadella became chief executive in early 2014, and the public stance reversed inside a year. The arc since then is easy to lay out:
- 1976: Gates’ open letter frames free copying as theft.
- 2001: Ballmer brands Linux “a cancer.”
- 2014: Nadella stands before a slide reading “Microsoft loves Linux.”
- 2016 to 2017: Microsoft open-sources PowerShell, Visual Studio Code and ChakraCore, and joins the Linux Foundation’s Platinum membership tier.
- 2018: It buys GitHub, the home of modern open-source work.
- 2020: President Brad Smith calls the old stance a mistake.
Customers Demanded It, So Microsoft Moved
The cleaner way to read that timeline is not as a change of heart but as a response to market pressure. By 2011 the warning signs were stacked up. Windows had lost the smartphone race to Apple’s iOS and Linux-backed Android. Amazon Web Services (AWS, Amazon’s cloud arm) was running away with the cloud. If Microsoft would not run Linux workloads natively, its own cloud business had no future.
A Microsoft executive later put the motive plainly, saying the company “had to embrace open source because customers demand it.” Not because it was right. Because customers demanded it. That single line explains more than any keynote.
Microsoft was on the wrong side of history when open source exploded at the beginning of the century, and I can say that about me personally.
That was Brad Smith, Microsoft’s president, speaking at an MIT event in May 2020. The confession was striking partly because Smith had helped run the earlier legal campaigns. Credit is due for saying it out loud.
Still, corporations rarely undergo moral awakenings. They respond to conditions. The honesty of the apology and the self-interest of the strategy can both be true, and here they are.
The $7.5 Billion Tollgate Called GitHub
Nothing shows the playbook better than GitHub. Microsoft paid $7.5 billion for it in 2018, and the bet paid off. The platform stayed open to everyone while the most valuable services built on top of it began routing straight into Microsoft’s commercial stack. You can keep your free public repositories; the money sits one layer up, in Copilot and enterprise plans.
The numbers since the deal tell the story:
- $2 billion annual revenue run rate reached by GitHub in 2024, with its AI assistant Copilot driving roughly 40% of that growth.
- 180 million-plus developers now building on the platform, per GitHub’s latest Octoverse developer figures.
- 518 million-plus public and private projects hosted, the raw material the paid tools sit on top of.
When Microsoft released the GitHub Copilot Chat extension under the permissive MIT license in 2025, developers cheered, and they were right to. The repository exposed the agent logic, the telemetry hooks and the system prompts. But the backend services and the large language models (LLMs, the AI systems that generate the code) stayed proprietary. That is the pattern in miniature: release what builds loyalty and counters rivals like Cursor and Windsurf, keep the part that prints money. Microsoft’s broader commercial momentum rides on exactly these high-margin layers.
Open at the Front, Billable at the Back
The clearest tell is hiding in the editor most developers open every day. The Visual Studio Code source is published under the MIT license as a project called Code-OSS, but the branded build you download from Microsoft is not open source. It adds telemetry, a proprietary license and the proprietary extension Marketplace, which is why the clean community rebuild VSCodium exists at all. The difference is spelled out in Visual Studio Code’s licensing FAQ.
Lay the major projects side by side and the design is consistent. The open part is genuine and useful. The proprietary part is where the value, and the dependency, lives.
| Microsoft offering | What is open | What stays proprietary |
|---|---|---|
| Visual Studio Code | Source code (Code-OSS) under MIT | The branded download, telemetry and the extension Marketplace |
| GitHub Copilot Chat | Extension code under MIT (2025) | The backend services and the language models |
| Azure Linux | The distribution, free and public | Most useful inside Azure’s paid cloud |
| .NET and PowerShell | Runtime and tooling under MIT | Best support and integration via the commercial stack |
What It Means If You Build on Microsoft Open Source
For working developers, none of this is a reason to avoid the tools. VS Code alone has done more for day-to-day productivity than most open projects ever will, and a lot of engineers run it without a second thought. The point is to know what you are leaning on before you lean hard.
A few practical checks keep the picture honest:
- Read the license of the build you ship, not the name of the project. Code-OSS and the branded VS Code are not the same thing.
- Know where the value sits. The backends, the language models and Azure are the paid layers, and they stay paid.
- Use the self-host paths where they exist. The open Copilot Chat extension can be pointed at non-Microsoft model backends.
- Keep the exits mapped. VSCodium, rival distributions and editors like Cursor are real alternatives if pricing or lock-in shifts.
The honest summary is that Microsoft has built two versions of “we love open source.” One means freedom. The other means a more elegant way to own the place developers gather. The same caution applies to Microsoft’s wider AI ambitions, where the open layer and the paid platform travel together.
If Azure Linux 4.0 follows the Copilot template, the next free release will draw more workloads onto the cloud that funds all of it, and the gift will have done its job before anyone reads the license.
Frequently Asked Questions
Is Visual Studio Code open source?
Partly. The underlying source code is published under the MIT license as a project called Code-OSS, but the branded VS Code build that most people download from Microsoft is not fully open source. It adds telemetry, a proprietary Microsoft license and the proprietary extension Marketplace. The community rebuild VSCodium strips those out.
Did Microsoft really open source GitHub Copilot?
Only the front end. Microsoft released the GitHub Copilot Chat extension under the MIT license in 2025, exposing the agent logic, telemetry hooks and system prompts. The backend services and the large language models that actually generate code remain proprietary and paid.
Is Azure Linux free to use?
Yes. Azure Linux, including the 4.0 preview announced in May 2026, is open source and free to download. It is built and optimized by Microsoft specifically for Azure, so its main practical value shows up when you run it on Microsoft’s paid cloud.
Why did Microsoft change its stance on Linux?
Market necessity, by the company’s own account. After losing the smartphone race and watching Amazon Web Services dominate the cloud, Microsoft needed to run Linux workloads natively on Azure to stay relevant. A Microsoft executive said the company “had to embrace open source because customers demand it.”
Does Microsoft still hold patent claims over Linux and Android?
Microsoft once claimed Linux infringed 235 unnamed patents and collected Android royalties from hardware makers, but in 2018 it joined the Open Invention Network and pledged its patent portfolio to protect Linux, which retired the bulk of that older threat.
How much of Azure runs on Linux?
Microsoft says more than two-thirds of customer compute cores on Azure run Linux, and core services including Microsoft 365, GitHub and OpenAI’s ChatGPT sit on Linux foundations hosted by the platform.
