Although it seems Microsoft and OpenAI have been deeply intertwined partners for a long time, they are only now getting around to releasing an official OpenAI library for .NET developers, joining existing community libraries.
The first beta of the effort is an OpenAI NuGet package supporting .NET 6 and .NET Standard 2.0, now at version 2.0.0-beta.2 and listing some 868,000 downloads.
visualstudiomagazine.com/Articles/2024/06/07/openai-net.aspx