Which versions of .NET are under a eula instead of an open source license?

The .NET Framework is the original implementation of .NET that has existed since 2002, and it is licensed under a proprietary EULA (End User License Agreement). In contrast, modern versions of .NET, specifically .NET Core and later, have transitioned to being fully open source under licenses like the MIT license and Apache-2.0.

The significant change to fully open source occurred with the introduction of .NET Core, which is a cross-platform and open-source implementation of .NET. This shift allowed for a more flexible development model and broader community contributions.

In summary, earlier versions of .NET (like the .NET Framework) were under a proprietary EULA, while the current versions are open source under licenses such as MIT and Apache-2.0.

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.NET Framework versions (1.0–4.x) were under Microsoft’s EULA and not open source. .NET became fully open source starting with .NET Core in 2014 under the MIT license, and all modern versions (.NET 5 and later) are MIT licensed.

Reference: https://learn.microsoft.com/en-us/dotnet/core/introduction