.CS File Format – Versions

Every version

C# 1.0 and 1.2

C# 1.0 had classes, structs, interfaces, events, properties, delegates, operators, statements and attributes. C# 1.2 made foreach dispose an enumerator that implements IDisposable.

C# 2.0

• Generics
• Partial types
• Anonymous methods
• Nullable value types
• Iterators
• Covariance and contravariance for delegates
• Separate accessibility for property getters and setters
• Method group conversions
• Static classes

C# 3.0

• Auto-implemented properties
• Anonymous types
• Query expressions
• Lambda expressions and expression trees
• Extension methods
• Implicitly typed local variables
• Partial methods
• Object and collection initialisers

C# 4.0

• Dynamic binding
• Named and optional arguments
• Generic covariance and contravariance
• Embedded interop types

C# 5.0

• Async and await
• Caller information attributes

C# 6.0

Released with the Roslyn compiler, which is itself written in C#.

• Static imports
• Exception filters
• Auto-property initialisers and default values for getter-only properties
• Expression-bodied members
• Null-conditional operators
• String interpolation
• nameof
• Index initialisers
• await in catch and finally

C# 7.0 to 7.3

C# 8.0

The first version aimed at .NET Core. Some features need runtime or library support that the .NET Framework does not have.

• Nullable reference types
• Readonly members
• Default interface members
• Switch expressions, and property, tuple and positional patterns
• Using declarations
• Static local functions, and parameters in lambdas and local functions that shadow outer names
• Disposable ref struct
• Asynchronous streams
• Indices and ranges
• ??=
• Unmanaged constructed types
• stackalloc in nested expressions
• @$ as well as $@ for interpolated verbatim strings

C# 9

• Records
• Init-only setters
• Top-level statements
• Relational and logical patterns, type patterns
• Native-sized integers (nint, nuint)
• Function pointers
• Suppressing the localsinit flag, module initialisers
• New features for partial methods
• Target-typed new and conditional expressions
• static anonymous functions, lambda discard parameters
• Covariant return types
• Extension GetEnumerator for foreach
• Attributes on local functions

C# 10

• Record structs and improved struct initialisation
• Interpolated string handlers
• Global using directives
• File-scoped namespaces
• Extended property patterns
• Lambdas with a natural type, explicit return types and attributes
• Constant interpolated strings
• sealed on ToString in records
• Assignment and declaration mixed in a deconstruction
• AsyncMethodBuilder on methods, CallerArgumentExpression
• A new span form of #line

C# 11

• Raw string literals
• Generic maths support: static abstract members and related features
• Generic attributes
• UTF-8 string literals
• Newlines in interpolation expressions
• List patterns
• File-local types
• Required members
• Auto-default structs
• Pattern matching Span<char> on a constant string
• Extended nameof scope
• nint and nuint as aliases of IntPtr and UIntPtr
• ref fields and scoped
• Improved method group conversion to delegates
• A warning for type names in all lower-case ASCII

C# 12

• Primary constructors for classes and structs
• Collection expressions and the spread element
• Inline arrays
• Default values for lambda parameters
• ref readonly parameters
• Aliases for any type
• The Experimental attribute
• Interceptors, as a preview feature

C# 13

• params collections
• The System.Threading.Lock type and its lock semantics
• The \e escape sequence
• Small improvements to overload resolution with method groups
• The ^ index in object initialisers
• ref locals and unsafe contexts in iterators and async methods
• ref struct types implementing interfaces, and allows ref struct
• Partial properties and indexers
• Overload resolution priority

C# 14

• Extension members
• Null-conditional assignment
• nameof on unbound generic types
• More implicit conversions for Span<T> and ReadOnlySpan<T>
• Modifiers on simple lambda parameters
• field backed properties
• partial events and constructors
• User-defined compound assignment operators
• Preprocessor directives for file-based apps

C# 15

C# 15 is the default for projects targeting net11.0 in the .NET 11 SDK. At the time of writing the latest SDK listed was 11.0.100-rc.3, from 25 October 2026.

• Collection expression arguments
• Union types
• Closed hierarchies
• Extension indexers
• Labelled break and continue
• Non-virtual static interface members on older runtimes
• Memory safety, as a preview feature

Choosing a language version

The default language version depends on the project’s target framework:

The <LangVersion> project property overrides the default. Its values are a version number, default or latestMajor (the latest released major version), latest (the latest released version including minor ones), and preview (the latest preview). Microsoft advises against latest, and a language version newer than the target framework’s default is not supported. #error version shows which version is in use.

Standards

C# is standardised by Ecma as ECMA-334 and by ISO as ISO/IEC 23270. The specification published on Microsoft Learn is the work towards a later edition, and includes newer features as they are added. It is the source of the clause numbers on these pages.

Microsoft keeps a version history and publishes a feature specification for each newer language change.