A post describing how to use GitHub Copilot in Visual Studio to migrate a .Net Framework application to modern .NET has provoked pushback from developers who found the old, free upgrade tool quicker and better.
Microsoft is busy adding Copilot seemingly everywhere it can think of, including developer tooling for upgrading .NET Framework projects to .Net Core. An existing .Net upgrade assistant extension for Visual Studio has been replaced with GitHub Copilot app modernization, which was made generally available in September. This new modernize agent can be summoned via Copilot Chat, and requires a Copilot Pro, Pro+, Business or Enterprise subscription. Attempting to use GitHub Copilot app modernization without the requisite license displays an error message.
Migrating from Windows-only .Net Framework is important for several reasons. One is that .NET Framework is maintained but there is little active development; the latest version is 4.8.1 from August 2022, which added native Arm64 support but not much else. Second, .Net Core (now officially just called .Net) is cross-platform, and runs well on Linux, reducing both friction and licensing fees for deploying to cloud platforms.
Senior product manager Mika Dumont posted about the new experience, provoking a quick response from developers. “Nowhere near ready for real world use,” said one, noting issues with upgrading an application from .Net Framework 4.7.2 including that “it tried to update our MVC [Model View Controller] and API controllers but ultimately failed … we had to manually update all the controllers” and that “we had 100s of hours of manual work to fix the partial upgrade of the projects.”
Another complaint is that the old upgrade assistant was superior. It was, said another dev, “a formalized process with clear, guided-through steps, and clear scope.” Copilot, by contrast, is “less performant, less formalized and deterministic, increasing risks.”
“New feature is a huge downgrade from the free option we previously had,” said another comment.
Although now hidden, the upgrade assistant is still available in Visual Studio 2026, via Tools – Options – Projects and Solutions – Modernization – Enable legacy Upgrade Assistant.
Pure C# or Visual Basic.Net code migrates easily to .Net Core, but many business applications were built using Windows-only features and third-party add-ons which are challenging to migrate, likely requiring substantial new code.
Separately, Microsoft previewed a service called Managed Instance on Azure App Service specifically for .NET Framework applications, at its Ignite conference under way this week in San Francisco, USA. Managed Instance is designed to support features which hinder migration to .NET Core, including custom COM components, Windows registry access, file share access via mapped drives, custom Windows services and more; admins can even get a remote desktop on a Managed Instance to get to tools such as IIS manager, event viewer and MMC (Microsoft Management Console) snap-ins, though the docs state that this is only for diagnostics and that persistent changes require scripts.
The introduction of Managed Instance shows the company’s recognition of the migration challenges, with or without AI.
Returning to the Copilot issue, part of the concern is that AI-driven tools are inherently more expensive to run, particularly when invoking cloud-hosted LLM (large language model) processing. If more free tools are replaced with subscription-based AI alternatives, costs will inevitably increase.