Microsoft took a landmark step at its Build 2025 conference, announcing the open-sourcing of its Windows Subsystem for Linux (WSL). The bulk of WSL’s source code is now accessible on GitHub, a development that fulfills a long-articulated desire within the developer community. This strategic shift allows developers globally to inspect WSL’s inner workings, contribute enhancements, and actively participate in the evolution of this key tool for running Linux environments on Windows.
The decision to open source WSL is particularly significant. Microsoft’s Pierre Boulay, highlighted the milestone, calling it “a great closure to the first ever issue raised on the Microsoft/WSL repo” regarding its open-sourcing, a reference to the posted GitHub Issue #1: Will this be Open Source?. For developers, this move translates to unprecedented transparency and the opportunity for direct collaboration.
Microsoft anticipates that this community involvement will be instrumental in WSL’s future, building upon past contributions that have already shaped the platform. Boulay emphasized this, stating, “This is why we’re incredibly excited to open-source WSL today. We’ve seen how much the community has contributed to WSL without access to the source code, and we can’t wait to see how WSL will evolve now that the community can make direct code contributions to the project.”
The open-sourcing is framed as an open invitation to the developer community, with a Windows Blog post noting the goal is to “unlock new performance and extensibility gains” and sending “an open invitation to the developer community to help us integrate Linux more seamlessly into Windows and make Windows the go-to platform for modern, cross-platform development.”
This major announcement follows a period of consistent WSL development, including the expansion of officially supported Linux distributions. Earlier in May Fedora Linux 42 became directly installable, after the official integration of Arch Linux in April.
Unpacking the Open Source Components
The open-sourced components of WSL encompass a wide array of critical elements. These include command-line utilities such as `wsl.exe` and `wslg.exe`, the `wslservice.exe` background service that manages the WSL virtual machine and distributions, and various Linux-side daemons crucial for networking and other core functions. WSL’s plan9 server implementation for file sharing is also part of the open release. Plan9 is a linux process that hosts a plan9 filesystem server for WSL1 and WSL2 distributions.
However, Microsoft clarified that certain components deeply integrated with the Windows operating system will remain proprietary. These exceptions include Lxcore.sys, the kernel driver underpinning the original WSL 1, and both P9rdr.sys and p9np.dll, which are responsible for the “\\wsl.localhost” filesystem redirection from Windows to Linux. Windows chief Pavan Davuluri explained that this open-sourcing initiative required substantial operating system refactoring to enable WSL to function independently, a change that now allows Microsoft to integrate developer contributions into the Windows pipeline more effectively, as reported by The Times of India.
WSL’s Evolutionary Path to Open Source
WSL’s journey to this open-source milestone reflects a significant evolution. The initial iteration, WSL 1, was first introduced at Microsoft BUILD 2016 and subsequently shipped with the Windows 10 Anniversary Update. It employed a compatibility layer to translate Linux system calls for the Windows NT kernel. A transformative update arrived in 2019 with WSL 2, which incorporated a genuine Linux kernel operating within a lightweight virtual machine.
This architectural shift delivered considerable enhancements in performance, system call compatibility, GPU support, and the capability to run graphical Linux applications. The Windows Developer Blogs further chronicled WSL’s development, noting its separation from the main Windows codebase in 2021 to facilitate more rapid iteration.
At the time of the open-source announcement, the latest version was 2.5.7, accessible via the Microsoft/WSL GitHub releases page. The open-sourcing now means the entire WSL codebase, including its functionality and the previously open-sourced kernel, is available for community contribution.
Broader Open Source Commitments and Future Outlook
Microsoft’s commitment to open source at Build 2025 extended beyond WSL. The company also announced plans to open source the GitHub Copilot Chat Extension for VSCode in the coming weeks and has already released ‘Edit’, a new command-line text editor for Windows written in Rust.
The open-sourcing of WSL is expected to foster a more dynamic and community-driven development ecosystem. Microsoft’s Pierre Boulay acknowledged the community’s pivotal role, stating, “WSL could never have been what it is today without its community. Even without access to WSL’s source code, people have been able to make major contributions that lead to what WSL is now,”
This move builds upon a history of continuous improvement, such as the WSL 2.4.8 update in December 2024, which enhanced support for modern Linux distributions and addressed key bugs. The technical architecture has also matured, with the adoption of a tar-based distribution model for Fedora 42, a method also utilized by Ubuntu and aligning with a Fedora Project proposal from late 2024.
With the core of WSL now transparent and open to contributions, the platform is positioned for accelerated innovation. Developers can explore the already open-sourced WSLg for graphical app support and the WSL2 Linux Kernel alongside the newly released WSL infrastructure. For further details on WSL components and architecture, developers can consult the official WSL development site.
