What Does Silverlight End of Support Actually Mean?
The short answer
Microsoft Silverlight reached end of support on October 12, 2021, per Microsoft's official lifecycle announcement. After that date, Microsoft stopped shipping security updates, bug fixes, and technical support for the Silverlight runtime and development tools. The product was not remotely switched off — it simply stopped being maintained.
That distinction matters, because it explains the strange in-between state many organizations found themselves in. An installed Silverlight application on a machine that still had a compatible browser could keep running the day after end of support exactly as it did the day before. Nothing expired. What changed is that every flaw discovered from that point forward stays unfixed forever.
End of support vs. end of function
It helps to separate three different events that people tend to blur together:
- End of mainstream development. Silverlight 5, the final major version, shipped years before the end-of-support date. New feature work had long since stopped.
- End of support (October 12, 2021). The formal lifecycle cutoff: no more patches, no more support cases.
- End of the browsers that could host it. Silverlight was a browser plugin, and it required a browser with plugin support — in practice, Internet Explorer. Microsoft retired Internet Explorer 11 as well, which is what actually stopped most Silverlight apps from loading. For many users, this was the moment the app "broke," not the Silverlight date itself.
What it means if you still have a Silverlight app
If your organization still depends on a Silverlight application, end of support has three practical consequences.
First, the runtime is frozen. Any security vulnerability in the Silverlight runtime discovered after the cutoff will never be patched. Running unmaintained software is a recognized risk category in its own right — U.S. government guidance on patch management, NIST SP 800-40, treats end-of-life software as something to plan around deliberately rather than tolerate indefinitely.
Second, the hosting environment is disappearing. Even where the runtime is installed, the browsers that can load it are retired or restricted. Keeping a working environment increasingly means keeping old software around on purpose, which compounds the first problem.
Third, the ecosystem is gone. Third-party control vendors, community forums, and tooling that once supported Silverlight development have moved on. If the app breaks in a new way, help is hard to find.
What it does not mean
End of support does not mean your code is worthless. Silverlight applications were written in C# and XAML, and both the language and the UI concepts live on in WPF on the desktop and Blazor on the web. Business logic, data models, and often a good deal of developer knowledge transfer to the replacements. The pages on this site walk through those paths — start with is Blazor the replacement for Silverlight if your app needs to stay in the browser, or when WPF makes sense if a desktop app would serve users just as well.