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After a year of shipping .NET standard 2.0, Microsoft has now announced .NET standard 2.1 yesterday. In all, 3,000 APIs are planned to be included in .NET standard 2.1 and the progress on GitHub has reached 85% completion at the time of writing.

The new features in .NET standard 2.1 are as follows.

Span<T> in .NET standard 2.1

Span<T> has been added in .NET Core 2.1. It is an array-like type that allows representing managed and unmanaged memory in a uniform way. Span<T> is an important performance improvement since it allows managing buffers in a more efficient way. It supports slicing without copying and can help in reducing allocations and copying.

Foundational-APIs working with spans

Span<T> is available as a .NET Standard compatible NuGet package. This package does not help extend the members of .NET Standard types that deal with spans. For example, .NET Core 2.1 added many APIs that allowed working with spans. To add span to .NET Standard some companion APIs were added.

Reflection emit added in .NET standard 2.1

In .NET Standard 2.1 Lightweight Code Generation (LCG) and Reflection Emit are added. Two new capability APIs are exposed to allow checking for the ability to generate code at all (RuntimeFeature.IsDynamicCodeSupported). It is also supported if the generated code is interpreted or compiled (RuntimeFeature.IsDynamicCodeCompiled).


There has been support for SIMD for a while now. They have been used to speed up basic operations like string comparisons in the BCL. There have been requests to expose these APIs in .NET Standard as the functionality requires runtime support. This cannot be provided meaningfully as a NuGet package.

ValueTask and ValueTask<T>

In .NET Core 2.1, the biggest feature was improvements to support high-performance scenarios. This also included making async/await more efficient. ValueTask<T> allows returning results if the operation completed synchronously without having to allocate a new Task<T>. In .NET Core 2.1 this has been improved which made it useful to have a corresponding non-generic ValueTask. This allows reducing allocations even for cases where the operation has to be completed asynchronously. This is a feature that types like Socket and NetworkStream now utilize. By exposing these APIs in .NET Standard 2.1, library authors now benefit from these improvements as a consumer as well as a producer.


DbProviderFactories wasn’t available for .NET Standard 2.0, now it will be in 2.1. DbProviderFactories allows libraries and applications to make use of a specific ADO.NET provider without knowing any of its specific types at compile time.

Other changes

Many small features across the base class libraries have been added. These include System.HashCode for combining hash codes or new overloads on System.String. There are roughly 800 new members in .NET Core and all of them are added in .NET Standard 2.1.

.NET Framework 4.8 will remain on .NET Standard 2.0. .NET Core 3.0 and the upcoming versions of Xamarin, Mono, and Unity will be updated to implement .NET Standard 2.1.

To ensure correct implementation of APIs, a review board is made to sign-off on API additions to the .NET Standard. The board chaired by Miguel de Icaza comprises of representatives from .NET platform, Xamarin and Mono, Unity and the .NET Foundation.

There will also be a formal approval process for new APIs. To know more, visit the Microsoft Blog.

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