Microsoft rolls out open source .NET 10 RC with big performance gains, but developers are questioning why essential tools remain locked behind proprietary walls.
Microsoft has released the first release candidate (RC) of .NET 10 under an open source model, complete with a ‘go-live’ license that allows production use. This long-term support release is heavily focused on performance improvements, with early results showing substantial real-world savings.
Microsoft partner software engineer Stephen Toub has published a 55,000-word report detailing performance optimisations in .NET 10. Highlights include thread pool queues that now complete tasks in just 4 ms compared to 20 seconds on .NET 9, and compression and decompression operations that run up to 65 percent faster thanks to zlib-ng integration. Gains extend across JSON processing, collection handling, JIT compilation, and cryptography.
The performance impact is evident in production. Ian Griffiths, Technical Fellow at Endjin, reported consistent throughput gains in his AIS.NET application, with increases of 9 per cent in .NET 9 and up to 27 per cent in earlier versions.
Another enterprise developer managing 20,000 servers noted, “In my company running maybe 20K servers on .NET, we get a 10-20 per cent CPU decrease every time we upgrade to the next major.”
Framework updates include tweaks to ASP.NET Core and Blazor, SQL Server vector search support in Entity Framework Core, and an experimental CoreCLR runtime option for MAUI on Android. Native AOT compilation continues in development.
Despite its open source foundation, .NET still faces criticism for closed tooling. One developer remarked, “It’s just a shame that an otherwise really well-rounded language still lacks first-party open source tooling. It’s unbelievable that in 2025 Microsoft still locks things as essential as a debugger behind proprietary licensing.”
The release works with Visual Studio 2026, due in November, but also runs on Visual Studio 2022. While performance wins are undeniable, the open source debate now centres on Microsoft’s ecosystem, where the runtime is free but key developer tools remain closed.
