C# History & Versions

How C# started

At the end of the 1990s Microsoft was building a new platform, .NET, for Windows and web applications. It needed a modern, object-oriented language that was safer than C++ and easier than it, with garbage collection and a rich class library. A team led by Anders Hejlsberg, the designer of Turbo Pascal and Delphi, created C# (pronounced "C sharp"). It was announced in July 2000 and shipped with the .NET Framework 1.0 and Visual Studio .NET in February 2002. C# is also an international standard (ECMA-334, ISO/IEC 23270).

C# code compiles to Intermediate Language (IL), which the .NET runtime compiles to machine code as the program runs. Several languages share that runtime, including F# and Visual Basic, and they can use each other's libraries.

For its first decade C# ran almost only on Windows. The open-source Mono project (2004) brought it to Linux and macOS, and Microsoft later bought Xamarin, the company behind Mono. Then Microsoft changed course: the Roslyn compiler became open source in 2014, and the cross-platform, open-source .NET Core arrived in 2016. Since .NET 5 (2020) there is a single ".NET" for Windows, Linux, macOS, mobile and the cloud.

Timeline of C# versions

Each C# version ships with a .NET release. The status shows the support of that .NET version.

1. C# 14Nov 2025Current

   • Ships with .NET 10 (LTS, supported until Nov 2028)
   • Extension members (extension properties and static extensions), the field keyword in properties, null-conditional assignment customer?.Order = order
2. C# 13Nov 2024Supported until Nov 2026

   • .NET 9 (STS): params collections, the new Lock type, partial properties, the \e escape
3. C# 12Nov 2023LTS until Nov 2026

   • .NET 8 (LTS): primary constructors for classes, collection expressions [1, 2, 3], default lambda parameters
4. C# 11Nov 2022End of life · May 2024

   • .NET 7: raw string literals """...""", required members, list patterns, generic math
5. C# 10Nov 2021End of life · Nov 2024

   • .NET 6 (LTS): global using, file-scoped namespaces, record struct
6. C# 9Nov 2020End of life · May 2022

   • .NET 5, the first unified .NET: records, init-only setters, top-level statements
7. C# 8Sep 2019Historic

   • .NET Core 3.0: nullable reference types, async streams, switch expressions, ranges [1..^1]
8. C# 7.0Mar 2017Historic

   • Tuples (int, string), pattern matching, out var, local functions
9. C# 6.0Jul 2015Historic

   • String interpolation $"Hi {name}", the ?. operator, nameof, expression-bodied members; first release on the open-source Roslyn compiler
10. C# 5.0Aug 2012Historic

    • async / await (C# made this pattern popular before most other languages adopted it)
11. C# 4.0Apr 2010Historic

    • dynamic, named and optional arguments, generic variance
12. C# 3.0Nov 2007Historic

    • LINQ, lambda expressions, var, extension methods, anonymous types
13. C# 2.0Nov 2005Historic

    • Generics, nullable value types int?, iterators with yield, partial classes
14. C# 1.0Feb 2002Historic

    • The first release, with .NET Framework 1.0 and Visual Studio .NET

How C# and .NET modernized

• Open source and cross-platform. Roslyn (2014), .NET Core (2016) and the unified .NET 5 (2020) turned a Windows-only stack into an open-source platform that runs everywhere and is developed on GitHub.
• A yearly rhythm. A new .NET and C# ship every November. Even-numbered .NET versions are LTS (three years of support); odd-numbered ones are STS (standard term, two years).
• Safer code. Nullable reference types (C# 8) let the compiler warn about possible null mistakes.
• Less ceremony. Records, top-level statements, global usings, primary constructors and collection expressions cut a lot of boilerplate; a small program can now be a single line.
• Performance. Span<T>, ahead-of-time compilation (Native AOT) and constant runtime work made modern .NET one of the fastest managed platforms.

.NET Framework vs modern .NET

Which version should you use?

• New projects: .NET 10 with C# 14 (LTS until November 2028).
• Existing projects: .NET 8 and .NET 9 both reach end of support on 10 November 2026, so plan the upgrade to .NET 10 now. Keep .NET Framework only for Windows apps you can't move yet.
• This tutorial: examples are compiled and run with the .NET SDK when we build the lessons, and their real output is shown under each example. C# examples can't run in your browser.

Official resources

• C# documentation and the C# version history
• .NET support policy: LTS and STS dates
• C# language design on GitHub and the Roslyn compiler
• ECMA-334, the C# standard
• .NET release schedule on endoflife.date

Last reviewed 21 October 2026. Release and support dates come from the official release pages linked above.