This content originally appeared on DEV Community and was authored by shiva shanker
Microsoft announced they’re open sourcing WinUI 3 (Windows 11’s native UI framework) in a 4-phase rollout starting October 2025. This is huge for Windows developers.
The Announcement
On August 2, 2025, Microsoft software engineer Beth Pan posted a detailed roadmap on GitHub confirming that WinUI 3 is officially becoming open source.
"Many of you have asked about truly open sourcing the repo.
While we're not ready to commit to a specific end date for
completing all milestones, we are actively working toward it."
- Beth Pan, Microsoft
For context, WinUI 3 is the modern UI framework powering Windows 11’s native apps, Settings app, Microsoft Store, and basically everything that uses Fluent Design.
Why This Matters for Developers
Current Pain Points
- Limited customization of Windows UI components
- Slow bug fixes for framework issues
- No community contributions to core Windows UI
- Fragmented Windows app development ecosystem
What Open Source Changes
Community bug fixes and improvements- Full access to source code for debugging
- Custom UI implementations possible
- Faster feature development through community contributions
The 4-Phase Rollout Plan
Microsoft isn’t just dumping the code on GitHub. Here’s their structured approach:
Phase 1: Increased Mirror Frequency 
Early October 2025
# More frequent commits from internal repo to GitHub
# Better visibility into ongoing development
# Still read-only for external devs
Phase 2: Local Build Support
git clone https://github.com/microsoft/microsoft-ui-xaml.git
cd microsoft-ui-xaml
# Build WinUI locally with proper docs and dependencies
./build.cmd
Phase 3: Community Contributions
# Submit PRs to the main repo
# Run tests locally
# Contribute bug fixes and features
Phase 4: GitHub as Primary Hub
- Issue tracking moves to GitHub
- Primary development happens in the open
- Full community engagement
Technical Challenges
The Complexity Problem
WinUI isn’t standalone – it’s deeply integrated with proprietary Windows layers:
// Simplified example of the challenge
class WinUIControl : public ProprietaryWindowsBase {
// This base class can't be open sourced
void RenderWithPrivateAPI();
void IntegrateWithShell();
};
Microsoft needs to:
- Separate open-sourceable components
- Create abstraction layers
- Maintain backward compatibility
- Ensure security isn’t compromised
Dependencies to Untangle
- Windows Shell integration
- DirectX rendering pipelines
- Security subsystems
- Legacy Win32 compatibility layers
What Developers Can Expect
Near Term (2025)
// Phase 1: More transparency
// You'll see commits like this more frequently:
// "Fix button focus ring in high contrast mode"
// "Optimize ListView virtualization performance"
// "Add new Fluent Design shadow effects"
Medium Term (2026)
// Phase 2-3: Local development
git clone winui-repo
// Build custom versions
// Submit bug fixes
// Test new features before release
Long Term (2026+)
<!-- Custom WinUI controls in community packages -->
<controls:CommunityDataGrid
ItemsSource="{Binding Items}"
CustomFeature="EnabledByOpenSource" />
Developer Community Reactions
Positive:
“Finally! This is what Windows development has needed for years. Being able to actually contribute to the platform we build on.” – @WindowsDev2025
Concerns:
“How many devs are actually assigned to WinUI? Feels like web is the priority and everything else is maintenance mode.” – @SkepticalDev
Pragmatic:
“This is great, but Microsoft needs to commit resources for community management or this becomes another abandoned OSS project.” – @RealistDev
Impact on Windows Development Ecosystem
For App Developers
// Current: Limited to what Microsoft provides
<Button Style="{StaticResource DefaultButtonStyle}" />
// Future: Community-driven improvements
<Button Style="{StaticResource CommunityImprovedButtonStyle}" />
For Framework Contributors
// Before: File bug, wait for Microsoft
- Bug exists for months
- No visibility into fixes
- Can't contribute solutions
// After: Direct contribution path
+ See the actual bug in source
+ Submit fix via PR
+ Faster resolution cycle
For Platform Competitors
This could accelerate cross-platform UI frameworks:
- Avalonia might integrate WinUI components
- MAUI development could speed up
- Electron alternatives might emerge
Timeline and Expectations
| Phase | Target | Developer Impact |
|---|---|---|
| 1 | Oct 2025 | More visibility, no contributions yet |
| 2 | Early 2026 | Local builds, better debugging |
| 3 | Mid 2026 | Community PRs accepted |
| 4 | Late 2026 | Full open development |
What to Do Now
If You’re a Windows Developer
- Star the WinUI repo
- Join the discussions
- Document your pain points – they might get fixed sooner
- Prepare for contribution opportunities in 2026
If You’re Building Cross-Platform
- Monitor the open sourcing progress
- Consider how WinUI components might benefit your apps
- Evaluate if this changes your UI framework choices
The Bigger Picture
This is part of Microsoft’s broader open source transformation:
- 2018: Acquired GitHub ($7.5B)
- 2019: Open sourced Windows Calculator
- 2020: Released PowerToys as OSS
- 2025: Now WinUI 3
# The evolution of Microsoft's OSS philosophy
git log --oneline microsoft/open-source-journey
a1b2c3d 2025: Open source Windows UI framework
d4e5f6g 2020: PowerToys goes OSS
g7h8i9j 2019: Calculator source released
j1k2l3m 2018: GitHub acquisition
Potential Concerns
Security
- More eyes on code = more security (hopefully)
- But also more attack surface visibility
- Microsoft’s security review process will be crucial
Fragmentation
// Risk: Multiple incompatible forks
WinUI-Community-Fork-1
WinUI-Community-Fork-2
WinUI-Enterprise-Edition
// Solution: Strong governance and compatibility standards
Resource Allocation
- Will Microsoft dedicate enough engineers?
- Community management overhead
- Maintaining backward compatibility
Conclusion
This is potentially the biggest shift in Windows development since .NET went open source. Microsoft is essentially saying:
“Here’s the UI framework that powers Windows 11. Help us make it better.”
For Windows developers: This is your chance to directly improve the platform you build on.
For the broader dev community: It’s another sign that even the most proprietary companies are embracing open source collaboration.
For Microsoft: It’s a bet that community contributions will accelerate Windows UI development beyond what internal teams can achieve alone.
References:
- Microsoft’s WinUI OSS Announcement – August 2025
- Neowin Coverage – August 2025
- Windows Central Analysis – August 2025
- The Register Commentary – August 2025
Discussion
What are your thoughts on Microsoft open sourcing WinUI 3?
- Are you planning to contribute?
- What features/fixes are you hoping to see?
- How might this change your Windows development strategy?
Drop your thoughts in the comments 
This content originally appeared on DEV Community and was authored by shiva shanker