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Yes—Microsoft made the main WSL project source available on GitHub on May 19, 2025. Developers can inspect the code, build WSL themselves, propose fixes and features, and participate in development through the official Microsoft/WSL repository. That is meaningful new control over understanding and contributing to WSL, but it is not ownership of Microsoft’s roadmap or proof that every WSL-related Windows component is open source.
What Microsoft announced on May 19, 2025
Microsoft’s Windows Developer Blog announcement said the Windows Subsystem for Linux (WSL) source code was available in the Microsoft/WSL GitHub repository. Pierre Boulay summarized the practical change: “You can download WSL and build it from source, add new fixes and features and participate in WSL’s active development.” See the May 19, 2025 announcement for Microsoft’s original scope and wording.
The repository lists an MIT license and contribution guidance, including paths for code, documentation and design proposals. Building from source therefore becomes an option for developers who need to inspect behavior, experiment with changes or submit improvements; it does not turn Microsoft’s Windows release process into a community-controlled project.
Which WSL components are in the released source?
WSL is a collection of Windows-side and Linux-side programs rather than one executable. Microsoft describes the open-sourced package as including:
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| Area | Examples and role |
|---|---|
| Windows command-line entry points | wsl.exe, wslconfig.exe and wslg.exe provide commands and integration from Windows. |
| WSL service | wslservice.exe starts the lightweight virtual machine and distributions and manages file-access shares. |
| Linux-side processes | Init and daemon processes handle startup, networking, port forwarding and related functions inside WSL. |
| Plan 9 server implementation | Supports sharing Linux files with Windows. |
| Related projects | WSLg has its own open-source repository, and Microsoft maintains a separate repository for the WSL 2 Linux kernel. |
Microsoft’s component list and scope are documented in WSL and Open Source resources. The repository’s source, issues and contribution instructions are at github.com/microsoft/WSL.
What is still closed?
The announcement did not open every WSL-related component. Microsoft Learn states: “The following components are still part of the Windows image and are not open sourced at this time:”
Lxcore.sys, the kernel-side driver used by the original WSL 1 architecture.P9rdr.sysandp9np.dll, which implement the\wsl.localhostfilesystem redirection path.
These remain in the Windows image, so the open repository is not a complete dump of all code involved in running WSL on Windows. The exact status above is the one Microsoft documented in its Microsoft Learn resource; it can change in a later Windows release.
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What “developer control” does—and does not—mean
What you can do
- Read the implementation instead of treating WSL as an entirely opaque Windows feature.
- Download and build the project, following the repository’s current developer instructions.
- Investigate bugs, create fixes, propose features and improve documentation.
- Submit changes for review and participate in issues and design discussions.
What you do not automatically control
- Microsoft’s roadmap, release timing or accept/reject decisions for pull requests.
- Closed components that remain part of Windows, including the drivers named above.
- Every behavior of the Windows-delivered WSL package; your locally built version can differ from Microsoft’s signed release.
In short, “control” means greater technical agency—visibility, reproducibility and a route to contribute—not ownership of the product or a guarantee that community proposals will ship.
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The open-source announcement makes more sense when WSL’s two architectures are separated. WSL 1, first shipped with the Windows 10 Anniversary Update after WSL was announced in 2016, translated Linux system calls through a Windows kernel component. WSL 2, announced in 2019, runs a real Linux kernel inside a lightweight utility virtual machine. Microsoft says WSL 2 improves Linux system-call compatibility and filesystem performance compared with WSL 1.
| Architecture | How it works | Practical implication |
|---|---|---|
| WSL 1 | Windows kernel compatibility layer implements Linux system calls. | Its kernel-side Lxcore.sys component was still closed in Microsoft’s 2025 list. |
| WSL 2 | Linux kernel runs in a lightweight utility VM alongside Windows integration. | Provides broader system-call compatibility and better filesystem performance, without making every Windows integration component open. |
Distributions can run as WSL 1 or WSL 2, and Microsoft’s documentation describes switching a distribution between those architectures. WSL is therefore not accurately described simply as “a virtual machine”: that description applies to WSL 2, while WSL 1 uses the compatibility-layer design. Microsoft’s background and architecture history are covered in the announcement and What is Windows Subsystem for Linux?.
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What this means if you want to build or contribute
- Start with the official repository. Use Microsoft/WSL and read its current build, developer and contribution documentation rather than relying on an old guide.
- Choose the behavior you need to study. Identify whether the issue involves a Windows command-line tool, the service, a Linux-side daemon, file sharing, WSLg or the separate WSL 2 kernel repository.
- Build in a development environment. Follow the repository’s stated prerequisites and build steps; a locally compiled package is for testing and development, not automatically a replacement for the signed WSL version delivered by Windows.
- Contribute through the project’s review process. The repository accepts code and documentation changes and points contributors to design guidance. Open an issue or proposal first when the change affects architecture or user-facing behavior.
Because some Windows-image drivers remain closed, source builds cannot necessarily reproduce every layer of the production stack. That boundary is a technical limitation of the 2025 release, not a failure of the repository’s contribution model.
WSL’s history in context
- 2016: Microsoft announced WSL, which first shipped in the Windows 10 Anniversary Update.
- 2019: Microsoft announced WSL 2 with a Linux-kernel-based design.
- 2021: Microsoft moved the newer WSL package out of the Windows codebase.
- November 2022: Microsoft says the package reached general availability as WSL 1.0.0.
- May 19, 2025: The WSL source repository became available publicly on GitHub.
What WSL provides on Windows today
WSL remains a way to run a Linux environment on a Windows machine. Microsoft’s documentation lists Linux command-line tools and applications, background services, graphical Linux applications through WSLg and GPU-accelerated machine-learning workloads among its uses. A compatible Windows host is therefore the basic hardware requirement; Microsoft does not specify a WSL-only laptop model or accessory in the cited documentation.
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Later developments should not be confused with the 2025 source release. In a June 2, 2026 Build post, Microsoft reported that community contributions had grown to more than 200 pull requests per month. That is Microsoft’s own reported figure, not an independently audited measurement: Build 2026.
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The same post described WSL containers as forthcoming to public preview. A subsequent Microsoft Command Line post said the container CLI and API were available through a WSL pre-release installed with wsl --update --pre-release: WSL container is now available for public preview. Preview status, supported versions and availability can change, so treat this as a separate, channel-specific feature rather than part of the May 2025 open-source announcement.
Frequently Asked Questions
Is all of WSL open source now?
No. Microsoft opened the main WSL project and related repositories, but it specifically listed Lxcore.sys, P9rdr.sys and p9np.dll as Windows-image components that were not open sourced at the time.
Can I build WSL from source?
Yes. Microsoft says developers can download and build WSL from the Microsoft/WSL repository. Use that repository’s current prerequisites and build instructions, and remember that a local build may not include closed Windows components.
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Does open source let developers decide WSL’s releases?
No. It enables inspection and contributions. Microsoft still controls its Windows releases, roadmap and decisions about which proposed changes are accepted.
The Bottom Line
Microsoft’s May 19, 2025 release gives developers real source-level access to WSL and a formal path to build and contribute, while leaving specific Windows integration components closed. It expands participation in WSL’s development without making the entire Windows-hosted stack community-owned.
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