Microsoft's C/C++ extension for Visual Studio Code (VS Code) no longer works with derivative products such as VS Codium and Cursor - and some developers are crying foul.
In early April, programmers using VS Codium, an open-source fork of Microsoft's MIT-licensed VS Code, and Cursor, a commercial AI code assistant built from the VS Code codebase, noticed that the C/C++ extension stopped working.
The extension adds C/C++ language support, such as Intellisense code completion and debugging, to VS Code. The removal of these capabilities from competing tools breaks developer workflows, hobbles the editor, and arguably hinders competition.
The breaking change appears to have occurred with the release of v1.24.5 on April 3, 2025.
Following the April update, attempts to install the C/C++ extension outside of VS Code generate this error message: "The C/C++ extension may be used only with Microsoft Visual Studio, Visual Studio for Mac, Visual Studio Code, Azure DevOps, Team Foundation Server, and successor Microsoft products and services to develop and test your applications."
Microsoft has forbidden the use of its extensions outside of its own software products since at least September 2020, when the current licensing terms were published. But it hasn't enforced those terms in its C/C++ extension with an environment check in its binaries until now.
(Microsoft's PyLance extension for Python coding is said to have exhibited this behavior for years, preventing its use in VS Code forks.)
Michael Truell, co-founder and CEO of Anysphere, which makes Cursor, said in the discussion thread two weeks ago that a temporary fix has been rolled out and a more permanent solution is planned.
"MSFT has a handful of extensions which are closed-source," he wrote, pointing to Remote Access, Pylance, C/C++, and C#. "The latest releases of the specific extensions no longer work in Cursor or other non-MSFT editors.
"Moving forward, Cursor is transitioning away from these extensions. We are investing in open-source alternatives which already exist in the community and will bundle these into the next version to enable a seamless transition."
Cursor allegedly has been flouting Microsoft terms-of-service rules for some time now by setting up a reverse proxy to mask its network requests to the endpoints used by the Microsoft Visual Studio Marketplace. This allows Cursor users to install VS Code extensions from Microsoft's market. Other VS Code forks tend to point to Open VSX, an alternative extension marketplace.
Truell did not respond to a request for comment.
Meanwhile, users of VS Codium are looking for free (as in freedom) and open source alternatives.
Developers discussing the issue in Cursor's GitHub repo have noted that Microsoft recently rolled out a competing AI software agent capability, dubbed Agent Mode, within its Copilot software.
One such developer who contacted us anonymously told The Register they sent a letter about the situation to the US Federal Trade Commission, asking them to probe Microsoft for unfair competition - alleging self-preferencing, bundling Copilot without a removal option, and blocking rivals like Cursor to lock users into its AI ecosystem.
Microsoft did not immediately respond to a request for comment. ®
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